Hard downshift from 2nd gear to first. A-833 4-speed.

did you:
check the bellhousing alignment to the crank?
use the roller bearing vs a pilot bushing?

typically the problem described is caused by too much centerline crank to transmission offset and using a pilot bushing vs the roller bearing, no lubricant fixes that.

As far a lubricants, do not use atf, use GL4 whatever, preferably a synthetic as the trans runs cooler, shifts better. Do not use GL5 lubricants. Sure motor oil works but so does atf.....btw atf is band aid for cold cold temps in manual transmission, it does not have enough lubricity for manual transmission and over time there will be worn parts. Passon used to make his own lube-if that is avail i would use that over anything else. I tried all sorts of lubricants as i had a very wicked 4sp car...

Manual trans cars should have the lubricant changed on a regular basis.
Bell housing alignment done when first installed.

Roller bearing as well when first installed.

I'm hoping its a rod adjustment but wanted some ideas before trying anything.