A suggestion on the head question. In the mid 80's Chevy made a 305 pickup engine that had decent 58cc heads. They were not the typical lightweight crap castings from that era. Some of the stock class dirt guys used to run them on 350's. I have an engine with them on it in my shop, but can't remember the casting numbers. I can check it out when I get home from work, if you want the info.

These heads would probably still be easy to find and would have hardened valve seats. The 58cc chambers would work well with the 283, but I would still calculate the compression ratio.