303 and 324 use the same deck height. The 371 and 394 have a taller deck height than the 303 and 324 engines. The 394 might have a weakness in the cylinder heads, and they have a tendency to crack. You'll probably need to have a stock cam reground. There will be some trouble finding a few things, but generally, you can find any stock parts you need.
Price is the problem.
Rod bearing and timing chains should be fairly easy to find locally for a good price. Kanter Products offers a complete line of parts to rebuild a stock 394. Exhaust manifolds also differ greatly. For headers try a custom header shop. There were differences between the 371 and 394, I believe in the port sizes.