A straight edge and good feeler gauges will work. Get the piston to TDC. You just need a very close estimate of where that piston is at TDC. Then you can figure out the c/r with what head gaskets and heads. Another option for heads is Marsh Performance. They will build your heads to what you need as far springs ect. Buying heads through a shop is better than bolting on without being checked out. PRH for your cam and he knows something about 383s.