from what i can see there is alot of little things would nice to have from 3rd gen..

Oil pan having more baffles to reduce lost of oil pressure form conitious direction of turn(if mr2's ever had the problem)

But as matt said about ecu ill take his word for it cause jetronic in genreal sucks ass

Intake manfifold seems better

Better head cooling may help detantion from the heating of exahsut vavles. Not sure I'm not big mr2 person.

Matt are exhaust side valves in head filled with sodium?

But all in all if you arent going motor crazy liek noshoes is.. As matt said get 2nd gen.

no shoes =