I have a aluminum bell housing for a A833 which would have been off a 74 E-body (#3743859). Can I use this in a 68 A-body without too much trouble? Or does it have more to do with the A833 year?

 

All A833's have the same bolt pattern to my knowledge, the DIFFERENCE comes in that some --specially the 18 spline--have a larger bearing retainer therefore bellhousings can have different size center holes

(Having said that, there does exist some A833 OD transmissions drilled for GM, I can't recall if they made 'em for Ferd 'er not. The GM OD unit I saw also had a special GM style input shaft)

I'm not sure about this last part---some E body bells may be bigger OD than your original A body, may be floor interferance.

(This was the case, example, between 69 and 70 RR. My 69 383 RR had a "real" 11" clutch, while my '70 used the horried 10.9 design. This used a 10 1/2" bolt pattern, modified cover, which would "drag" on the outer fringe of the disk as it wore. This was to allow a smaller bell in the car)