well i can help out a bit.....
T3 turbo's are the pretty much standard bench point in the aftermarket import world of hondas. T3 is the exhaust side of the turbo, but they have mated it with a slightly larger t4 compressor housing to give the best of both worlds since a honda would struggle immensly to spool up a straight T4. then they have different trims (AR etc) and ball bearing and non ball bearing. they have "B" trims and "E" trims the "E" is slightly smaller for quicker spool up.
onto the Mitsu's these are mostly your "G" series turbos
16g, 18g, 20g
most of these are internal wastegates, but the more built ones are usually external waste gate operations. GReddy also runs some of these, but they mostly use the TD04's etc etc
as fot the rest of the "T" series, these are all turbonetics for the most part, its just their classification of sizing that the rest of the industry has adopted. T25,T88 etc etc, the size is what changes here
hope that helps
shed some more light on the topic if anyone knows!