best cylinder head

Any work done to the X heads? If they are just stock they will flow in the 215 CFM range. Usually the flow tips over at about .500 lift. Maybe a little less. So the head's are holding you back for sure. Carb is small too. 850-950 double pumper is best. No vac secondary with that cam.

As for "good" heads. There are plenty. Ideally what you want, is a head that has max flow that is similar to your cam. For ex if you cam runs to .550, then your head should flow to at least that. Given your cam spec range. You can see here how the heads are holding you back. You don't have the flow from the heads that the cam can do. You're basically "wasting" .150 of lift. I would suggest aluminum heads. Get something that flows MINIMUM 270 CFM around .500 or more. Anything less can be achieved with X/J heads anyways. Make sure they are milled to keep compression up. You ideally want 8.5 DCR (dynamic compression ratio) if you're on pump gas, based on zero altitude. Higher up you can get away with more. With access to better octane, you can do more.

In my opinion, I think you got a very valid setup to test edelbrock victors on. If you got those kinda pennies.