I have put the Crower Level 3 in a 62 Skylark 215. And I have put a Crower Level 2 in a 61 Olds Cutlass 215. Both worked fine. The level 3 was lopey-er of course..
Flowmaster’s give you a little lopey sound all by themselves. I’m going to try some Flowmaster HP2s(Hush Power) soon but don’t know if they have the same effect as standard Flowmaster.
Also, if you go to a stiffer valve spring on a level 2 cam you will get a little more lope than the standard springs and stay with the driveability of the level 2.