The problem here is that the original part, an overly-complicated two piece assembly, is made of rubber. Old rubber. Newly-manufactured parts are simply not available, and there is no substitute from other years. New-old-stock parts are available; mine lasted four (4) days before splitting (I actually drive my car, on real roads; they're probably OK for a museum car). This design was used only on the early cars; I believe the design was changed to the more typical two-piece rubber job in 1965. (In the photo on the right, a blown-out factory bushing is compared to a "late model" style bushing.)
For such a simple part, I spent an awful lot of time getting this right!
I can personally attest that no matter what anyone tells you, 1965-up strut bushings do not and will not fit. 1965-up strut rods will not fit either. (The length is correct, but the angle of the tang that bolts to the lower arm is incorrect.)
(For comparison purposes, take a look at modern-type strut bushings in various states, in my 1970 Hornet.)
The solution requires some machining of plastic parts; it can be done on a drill press.
To summarize before I get to the details of my solution:
The problem is that the installed thickness of the original strut bushing is
very thin, approximately 3/4" to 7/8" thick (measured from the dished "washer"
to the strut bushing bracket). The more-modern system uses a bushing that is
2.5" thick. Even if you managed to cram it in there, it would exert tremendous
forward force on the lower arm, dangerously stressing the thin inner end, and
would put off-axis force on the trunnion. Don't go there and do that.
It seems obvious to cut down a modern replacement to the correct thickness and I did just that; and it worked great for a day or two. I was surprised at the results, which you can see here.
Basically, the overall strength of the cut-down bushing plummeted, the over-3" dished washer pushed through the 1" center hole! Once this happened, turning the wheels lock to lock would push the dished washer in and out of this small hole; quite a sight!
My solution is to retain the modern two-piece bushing design, but to use suitable materials to get the necessary strength. The new bushing design had to be short enough to maintain proper geometry, but strong enough to absorb the substantial energy that strut bushings are meant to absorb.
The trick was to use different materials for the front and rear halves of each bushing pair; the front half is a modified urethane aftermarket part, the rear stock rubber.
The front bushing half maintains correct geometry, and works as new designs do (eg. the dished washer is concave-side-rear; stock 1963 is convex-side-rear) and transmits forward energy (like whacking a curb) to the chassis. The rear bushing being rubber deforms as necessary as the suspension travels up and down, and since it is of stock thickness, is strong enough to survive when rear-directed energy (eg. potholes in reverse, lock-to-lock, etc) is applied.
There are two other minor problems with this arrangement: One, the overall, assembled length is longer than stock (short urethane in front + stock rubber in rear), therefore the castellations on the big nut don't reach the cotter hole. The fix is to use the modern-style steel inner sleeve, supplied with both bushing kits, cut down to 1-3/4" (CHECK THICKNESS!), replace the castle nut with a plain nut, and use Loctite. Two, urethane groans. It's surface durometer is so much higher that it grabs the bearing metal parts, and oscillates like a tight string. The method I used to make the bushing (below) creates a surface that groans less than a smooth surface, but it isn't silent. Greasing makes it so, but doesn't last. Some have suggested drilling the dish washer for a grease fitting, but the effects of lubing it seem only to last a week or two.
I purchased two sets of bushings; a stock set for application 80-83 Concord, MOOG #K3090, Perfect Circle #FA685. These should be easy to find. I also purchased a set of urethane bushings, but I neglected to record the part number; they are dimensionally identical to the stock ones above and are also a Jeep part; nearly any late (1980+) urethane strut bushing should be correct. Note that it MUST be urethane!
By measuring two other assembled 1963 cars I determined the approximate installed effective length of the front half of the bushing to be 3/4" to 7/8". Since urethane compresses very little, I cut down a urethane bushing half, one for each side, and shaped it to fit.
First I sawed each bushing in half, saving the "inside" portion, the part with the step that fits into the bracket on the chassis. I cut it approximately 1" thick with a cutoff saw in my mill-drill; I clamped the steel inner sleeve (that comes with each bushing kit) into the vice so that it stuck up about 3/4" and pushed the bushing stepped-part down onto it. This kept it flat and level as I cranked the table horizontally against the cutoff sawblade. You could probably achieve a less precise result by claming the sleeve in a vice horizontally and cutting the bushing with a hand hackshaw, rotating the bushing as you go.
(To the left is the completed bushing assembly prior to installation.)
Next, I chucked this half into my mill-drill (a drill press will do). Chucking urethane ain't easy -- obviously it deforms if you squeeze it. What worked for me was to use a 1" mill bit and just jam the bushing on it; then I ran the bushing-jammed-into-bit down so that the bottom of the bushing ran against the top of my big vice, opening the jaws such that it straddled the stepped backside of the bushing, and applied oil, and turning the motor on. The bushing ran nice and smooth and flat across the vice top surface.
Then I took a three-cornered knife and radiused the top of the bushing to match the concave part of the strut rod dished washer. Basically I rocked the knife over the bushing, cutting off material until it looked right, removed it from the mill-drill and checked against the washer, and repeated as necessary.
Here you can see the assembled unit; note the unsymmetrical bushing thicknesses. However, geometry is now perfectly correct, the urethane part should last a long time, and since the original design and metal parts are retained, it should be as safe as stock.