I can say my bit about the 4JB1 T now.
I picked one up this week in a UBS55, to use as a donor vehicle. It's not intercooled (a few were here in Aus from what I can tell). I picked it up interstate and drove it straight home - nothing like a 1500km journey to see how it goes! Just over 9km/litre. I don't know what that is in mpg, but it's bl#@dy good. With chunky mud tyres the 4JX1 was getting 14.1 km/l. I'm happy. I've just got to get it into the MY2000 now.
i haven't started yet, but the bellhousing on the UBS appears to be cast in 1 piece with the gearbox housing. If the bolt pattern is different, I could be looking at custom making an adaptor plate, figuring out input shaft length/spigot match-up etc...man I hope not!