Best Electronic Ignition Setup for a 273

Looks like you already have a distributor. Get a Pertronix kit and convert it would be the easiest and probably cheapest way to go. If you want to have the '72-up factory electronic, you'll need a distributor, ballast resistor, module, wiring, etc. I think you'd be better off with the Pertronix unit, especially if you like it to look stock.