"Barkleydave" -
'Not doubting your frustrating experience with a non-fitting rear transmission seal kit, but it seems odd that the seal couldn't be installed on your '29. Had the back of your case been somehow altered, possibly a crack welded that was not ground smooth? That would definitely interfere with the new seal's fit. Or too much grease/paint/road grime build-up?
Also, you probably noticed that the seal cover has one corner that is slanted. This slanted corner has to go in the upper right orientation, meaning towards the U-joint, on top. If you tried to install the cover with the sloping corner on the bottom, it won't fit because the standard non-sloping corner comes into contact with the U-joint lower clamshell. I assume you tried the cover both ways?
You also have to put the bolt in the cover when you place the cover over the shafts. If you try to put the bolt in after the cover is glued to the transmission case, you can't get it in, as I recall. An ear on the lower U-joint clamshell blocks the bolt's pathway. It's been a while since I installed one of these seal kits, but I know that I made mistakes initially by trying to put the cover in place in the wrong orientation and by neglecting to place the bolt inside the cover before placing it on the back of the transmission. I learn more by making mistakes than by doing things right the first time.
Could either of these situations have been the problem in your case? Otherwise, I have never heard of this excellent kit not fitting a Model A transmission case. Something ain't kosher here.

By the way, my suggestions assume that the transmission is still in the chassis and not on an engine stand. To ensure that the seal is not installed improperly, it's a good idea to check it against the lower U-joint clam shell while the engine/transmission are still on the stand. Yes, you can put the seal in upside down like this if the lower clamshell is not in place. You'll discover the error when you go to mount the clamshell and it is obstructed by the non-sloping corner of the seal cover. I always thought it would be a good idea if the manufacturer sloped both opposite corners so that the seal installation would become idiot-proof - if there is such a thing. Or maybe the part is being made that way now? 'Dunno. 'Haven't installed this kit in a few years.
Marshall