2rz= Less power, less displacement, doesnt have balance shafts i think? which is good and are usully cheaper and easier to find.
3rz= depending on where your from they can be hard to find for a decent price. here in az they dont come around too often.
Never driven a 2rz swap but my 3rz is a nice improvement over my old 22rte motor. But apparently the torque difference between the 2rz and 3rz is what makes a noticable difference.
If you want as much power as possible then wait for a 3rz, but if you just want a better performing motor than a 22r then get whatevers cheaper, more complete, lower miles,easier to find.
Dont know the physical differences since they look pretty much identical
Why spend extra money to turn a 2rz into a 3rz, just wait for a 3rz if thats what you want
Lots of people have done 2rz swaps and are happy with them
Guy here in az just did a 2rz swap in his 86 4x4 and is happy with it, no reason you couldnt or shouldnt do it with 4wd.