I believe the M10 will actually respond quite well to ST rules. That in a 84 318i chassis would be fairly decent. Suspension has been figured out, brakes are decent, engine is bulletproof.
But, now I'm looking at the S14 that was in the M3, or maybe a Cosworth YBF from an RS escort!! I figure a $15k build on a S14 motor will be good for 350-370hp.