Quick question for the Brain Trust re: A833 countershaft interchange

I've been a Saturday-Sabbath guy for about 25 years now

Overdrive pins are shorter to allow for the front cup plug. I have not measured the front ends to see if they are the same as the standards. If they are then they can be used in the older boxes.
But
That key does nothing but keep the shaft from spinning.
Loc-tite will do that too.
Your choices are;
Stick the original shaft back into the box with a good key, and the broken part to keep in place, and send it.
or
if you lost the broken piece, use whatever, to keep it in place.
OR
What I have done, is flip the pin 180 and grind a new slot, badaboom, with a die-grinder. It doesn't have to be pretty, cuz nobody is ever gonna see it. The bonus to this is that, it flips the normal-wear surfaces as well. Just don't make the cut too deep.
BUT
If you have an OD box and try to use an Early long-pin, well, the front hole is loose to allow oil into there to be a noise reduction gimmick. Consequently, there has to be an expansion plug installed there, to prevent leaks. So, no room for a long pin and no loc-tite will last for long.
Now
your choices are;
1) shorten the pin, or
2) do what I did, which was to fabricate a steel bushing, and machine the od case to accept it; then size the hole for a light press-fit on the pin.. and thus you eliminate that IMO, dumb idea.