To attempt to put the wealth of info in to one place...
A little goes a long way with these motors. A good combination to get a pretty good motor would be: ARC #6282 billet rod, DynoCams 245 cam, and 18 pound valve springs with matching retainers and keepers.
- ARC #6282 is available through OldMiniBikes. Just search for it and it will appear. It's made for the Tecumseh OHH series of motors (OHH50, OHH55, etc...) but it fits in the HS series just fine. Remove the governor once you have this rod installed.
- DynoCams does not list the 245 cam on their website, but just call them and arrange for a regrind of your stock cam. It costs about $100. They do list the valve springs, retainers, and keepers, those are DCS-AN for the springs, DCSH102 for the retainers, and DCSH103 for the keepers. The retainers will have to be milled or filed down on the inside, as they are made for dual valve springs.
Pictures of the motor and the flywheel can help to decide where to go from here. Timing is completely different for points motors vs CDI motors. Also, if you are running a steel points flywheel, I suggest re-epoxying the magnets back in place on the flywheel. 40 year old glue and 5,000+ RPM's do not mix well!
There are a few other threads of builds. A quick browse of the Tecumseh forums will bring you some great results.