IMO, staying with stock springs is a BAD idea. A 40 yo spring may not even be adequate for a stock cam. I had a 71 RR that would float the valves hard at 5200rpm. That was 20 years ago. When we took the heads off, it looked like it had tiny valve reliefs on the tops of the stock low compression pistons. About the converter, a converter change is one of the biggest performance improvements you can make.