[MKS427]

Carroll Shelby originally wanted the aluminum 390 FE for the S/C. NASCAR would not give them up. That said, he was probably looking for to keep the car balanced and get as much power as possible.
If your Classic Roadster has a 96 inch, wheelbase it would throw off the weight bias relative to a 90 inch wheelbase car. In which case you might want to consider a lighter power plant, if you desire better handling.
I was considering a big block, but only if I could get a hold of one of the aluminum Ford blocks that are no longer in production. I ended up going with an iron Dart block stroked to 427. I built it to have better low-end torque numbers versus high-end horsepower. I am very happy with it.
Whatever you decide I am sure you will enjoy. Probably the best recommendation, is just to make sure it will be reliable on pump gas.