went to a better internal coating for slightly less wear, also required less lubrication, so they went from 4 oil injectors on all previous models to 2 on the FD. Smooth port exhaust sleeve, same as s5 NA in all other regards.
yes, you can mix and match housings of all kinds, this is the beauty of 13B engines after 86. You can purpose build an engine for many different requirements because of this. You can do complete rotating assy swaps, change irons for different intake port configurations, or improvise out of necessity.