Yes, in most cases. the lowers are pretty much al the same length. The difference is in the length of the stanchions and carts / shafts of the internals.
You wouldn't want to use 140mm stanchions with 100mm internals from different eras just in case the stanchions bottom out in the lowers and stick there or something else weird happens.
Current 140mm forks will adjust down to 100mm though, so if the 2 donor forks are of similar length travel and you want to swap lowers or stanchions, it should be ok.
Try them out by fitting them together before rebuilding the forks. set them at full compression and full extension to check the bushing overlap is right.