Just remember that early B/RB's used a smaller diameter pushrod, so the lifter cups will be smaller for original lifters, pretty sure the cup in the rocker is too but it's been 20+ years since I had my hands of a set of early rockers.

I do know I ended up running a set of early pushrods with later rockers and lifters without issue, but you cannot go the other way (early lifters/later pushrods).

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.