You cn do it all yourself.
Here is a free download compression ratio calc.
Download Free Compression Ratio Calculator, Compression Ratio Calculator 1.0 Download
You need to know the cylinder head cc and the piston to deck clearance @ TDC
Generally (based on a 0 deck height) 383 with a 64cc head wants a -12cc dish
a 70-72cc head can use a 383 flat top piston.