Regarding the front drum to support bushing - there are two reaction shaft support bushing sizes from 1962 - 2008, narrow and wide. The metal seal ring spacing never changed on the wide bushing support.
I think you can install the wide bushing drum on a narrow bushing support and the unit will assemble
The ring spacing did change to compensate for the wider bushing. Narrow bushing drum will fit on wide bushing support but ring location will be wrong. Wide bushing drum won't physically fit on narrow bushing support.
Thanks for posting the photo. That was what I was trying to explain.
Relocating the vent is not really a band-aid, it just removes one possible source the fluid can come from in the bell housing area.
I usually only noticed small amounts of ATF that got out of the vent with high RPM runs.
If your dumping alot of fluid, then there is other problems.
Either way, the trans is going to have to be removed.
Might be able to remove the valve body and air-pressure check the trans, to see it you can hear leaking from the converter or pump housing area.
I think some of the pumps front bolt holes are open to the inside of the case, so a loose bolt (not sure how bad the leak would be if missing the sealing washer?) or stripped case threads could result in a leak, along with the plug for the front band pivot shaft.
And that is if the leak is not from the pump seals, gaskets, or converter.
