Morel 5321 lifters...

I used the same lifter in the 273 for my 65 Barracuda. My machinist made sure they all had good clearance before the block left his shop. Mine will install and remove with the heads on, but you gotta hold your mouth just right to do it! I don't know why it would make a difference, but I had to get my lifter bores bushed because a few were too big.