hey up beesa bloke
i've had both, the type 01 is all round a larger gun than the ordinary 50 and from memory, nothing will actually fit, the trigger is completely different in that the early 50 has three ball bearnings for the sear, the latter 01 doesn't, the cylinder is a larger diameter, the stock is much chunkier too.
from (older) matierial that i've read, the earlier, slimmer one is preferred but my fave of the two was the 01 handfull.
the mainspring on my type 01 broke, it took bleedin' ages to strip, anyhow, i cleaned all the gunge out and fitted an ox spring and to be honest, it didn't really seem to make much difference but i didn't have a chrono for before/ after comparisons
all in all, they are a really nice quality rifle, in fact all original stuff is excellent gear being well made and finished off very nicely
hope this helps, oh and welcome to the madhouse
john