Andy,
You can use the larger clutch and flywheel assembly (no starter problem if both were used with 6 volt starter). You might want to get the flywheel resurfaced (about $40 at NAPA or other machine shop). If the clutch disc and pressure plate surfaces look good, you could take a chance with them. Same with the throwout bearing and the crankshaft pilot bushing.
But, if you want to play it safe (I would), a full clutch kit costs $150-200 and it would include a clutch disc, pressure plate, throwout bearing, pilot bushing, and clutch disk alignment tool.
You are correct about the 4-speed being a simpler shift mechanism compared to a 3-speed. You will most likly find that you will hardly ever use 1st gear (but, so what). The four speed can be a little uncomfortable if you want three people in the front seat.
Tim
