yes a 4age head would make a fair bit more power, the advantage of using the 4ac head is its cheaper and also less mucking around with electrics as you would be able to run it all with standard loom.
although 4age head and carbs just running on dizzy with locked out timing wouldn't be too much of a hassle. I've been reading up on megajolt junior ignition system, seems to be the go for running carbs without a dizzy. Not too expensive, and you can fully program ignition curve, vaccumm advance and some other stuff. makes it a bit easier to tune