Ballast resistor-> 4 prong to 2 prong

IMO, msd is obsolete. You have to buy a dumb timing light and a timing retard controller is expensive and ugly. Have to dick around with timing tape. And apparently there's a load of counterfeit units so that's sketchy. It's only good for a hot, capacitive discharge spark til 3000 rpm or so. It's still controlled by springs and flyweights so what's the point? You'd see more power and drivability by using a modern ignition driver like megasquirt in "ignition control only mode" with a Bosch driver and controlling several variables to create your own ignition curve. Want to retard timing on start? No problem. Retard timing when eng temp is too high? Ok. Valet parking spark cut above 2500 rpm? No problem. Set your own coil dwell. Flood clear on startup with a throttle position sensor? Little more work but it'll do it. Control cooling fans, nitrous, etc. The days of swapping springs and adding limiting plates and grinding off metal are over. Adjust any ignition timing on the fly on a running engine with a 3D ignition map. The controller is smaller than msd and hides under the dash with simple inputs from the distributor you already have that you fully lock out.

- The msd box in my avatar went into the garbage