Horsepower guess?

The stock pistons will be waaay down the hole. Even with magnum heads you will be lucky to get 8.5 to 1 compression. For a cam I would thick long and hard about the XE262 Comp Cams. Lots of low end, decent lift with the 1.6 rockers and vacuum to run power brakes. It will definitely work with a stock converter.
I run a cam similar to the XE268 with more compression and the stock converter and power brakes worked fine......