Short and sweet. I have a set of Ga heads and a set of C heads. What is my best overall option for the 455 rebuild? Any distinct advantages or pitfalls? Forum gurus, do your magic.

 

With the exception of the J heads, all the heads flow similar. The G heads have the advantage of hardened seats, but unless you really plan to work the engine like it owes you money, then stock unhardened seats isn’t that big a deal. Use whichever are in the best condition.

For the best bang for the buck, aftermarket aluminum!

 

Check the spring seats on the two sets of heads. The Ga heads are probably deep spring seats while the C's are probably shallow spring seats. The Ga's probably used valve rotator retainers - hence the deeper spring seats.
Either set of heads come in both big and small valve versions. Both can be converted to big valves if desired.

The valve spring pockets are probably the biggest difference between the two sets of heads.