That's why I said I think I may have had a proto-type or something. The copy I had a long time ago had the elves deciding what class each time between Fighter and Magic-user.
For those of us that were fairly young when we stepped into the world of AD&D, BECMI & B/X were easier to understand than the shambolic AD&D. I know a lot of how we ran AD&D was based on BECMI with AD&D rules bolted onto it.I think this was pretty common, especially if your group were kids. I started on B/X in 1981 but quickly moved to AD&D, but still used all those B/X modules and even monsters pulled from the B/X book if we had it handy and not the MM laying around.