Honestly ... you'll get all kinds of replies that are gonna be different
The key thing to understand is what kind of rockers and heads you are using
on your combo
Rockers come in all sizes and shapes
and
I'm NOT talking about ratio here but more so ... size of rocker
I use stud mount Scorpion's and they are really big

so
I had to remove a bit of material from the bosses
and
I had to remove the baffle
The heads can be different as well cause some have a taller or shorter lip
that the vc is sitting on thus causing more or less room.
I cut the filler neck in half and used a small radiator hose from some little ricer
car to slightly raise and tilt the top half of the filler neck for the clearence I
needed for my application.
I needed about 1/16 of an inch more room between the vc and alt
so I used one very thin washer on each alt bolt to shim out the alt just a tiny bit cause .....
I didn't like the idea of grinding on things
I guess I'm trying to say ... Put in on and modify as needed
Grady