I've seen an '87 in the junkyard with the 4 cylinders.
Turboing a 4 cylinder that's in a car is totally different than turboing a 4 cylinder in a 4,000LB rolly polly olly SUV. You need torque down low, not up high waiting for boost to hit. Boosting the stock V6 is a WAY better option than swapping in a KA. They made the Z31 300ZX with turbos, their engines are almost identical to ours. Same rods, bearings, block, etc the only difference is the compression ratio was lowered to 7.8:1 from 9.1:1. It'll be incredibly snappy and have a hell of a lot more torque if you turbo the NA engine due to the higher compression ration, and at 10-11PSI you can easily hit 250HP.