Many have adapted the HEI from the 75 & on six to the 235. Shorten the shaft and adapt the clamp, Tony (from NY) does it with a grinder, but he's an old bike hacker. Here in Kansas the used HEIs are getting scarce, last one I saw they wanted $65 for. Another option is to put a Pertronix ignition in your distributor. Works good if your distributor isn't worn out. Roughly $80 for the module.
As I said, the rear gear change is the most bang for your buck. Last price I was quoted on a 4.10 pumpkin was $75. Find one from a 64-72 3/4 ton. If you search the archives you'll find a lot of good info on both subjects.
