1974 Brain Box saves the day.

The TO-220 transistor would likely work if they properly heat-sinked it. That is what the big screw-hole is for, and you see them bolted to a thick heat-sink in every commercial product. As 67Dart273 suggests, for a factory look, gut the box and hide a GM 4-pin HEI inside (search posts). It needs heat-sinking too and a ground connection thru its case. For best look, gut an OE ECU. If you don't care about factory look, use a GM 8-pin module and coil. A factory GM cable connects the two. Easy pick from a 1985-95 GM V-8 truck, and many posts here. You can then toss your ballast resistor. Your Mopar e-distributor can trigger it. Stronger spark, so might need 8 mm plug wires. You can grab good silicone plug wires from a Mopar Magnum V-8 to fit a small-block. They are nicely labelled by cylinder.