any of the main conversions are fine
16v 4age
20v 4age
Beams
CA18det
Sr20det
Formula Atlantic 4age <--do it!!!!
being USD, quad setup have no clearance issues as brake booster is on the other side, so i would lean towards a more NA quad setup taking advantages of that + it keeps it really original with the 4age motors
16v or 20v, or something with more power the beams with quads
beams and ca18det/sr20det all will cost roughly the same, as whole transmission needs to be upgraded/changed, unless you got the hook ups for cheaper parts
Formula Atlantic 4age cost more then most working JDM AE86, but do it cause its the shit! =D