Easy fix...
89> Sigma
90> Stealth
90> Galant
90> 3000 GT

Basically, ANY Mitsu from 89 up will plug right in there with oil pan, oil pump setup (with filter boss), harmonic balancer, timing covers, intake, exhaust & all front accessories.

I have a Stealth engine in my 89 Raider. I would suggest while that deep into stripping the engine, FULL gasket set, WATER PUMP, check water pump pipe, CHECK ALL LIFTERS (temporarily unseized 5 lifters in my engine this weekend) & for a tad of insurance, throw some crank & rod bearings in the block.

Further, rework the heads & maybe use the cams from monty.

Ed