It takes more than just any generator right half, it must be a knuckle right, because not only are the tappet block holes different, but there are vacuum galleries that are not drilled in later cases. These are critical for draining the oil from the valve cups. In Pan and later motors, this passage from the breather is relocated to blow instead of suck. If you really wanted to badly enough, the casting of '48 pan cases still had the bosses that could be drilled and plugged (but why?). Older S&S literature showed knuck heads altered for external drains, which would allow for any right case, however your pushrod covers may not seal very well, as the later tappet blocks are angled differently for pans and differently for shovels too.