421 sbc AFR 220CC heads, ported super victor intake, Pro Systems 1250 carb, looking for carb spacer recommendations. 1" ? 2" ? none? Thanks,

It's possible that you might need more plenum volume but only testing can tell you for certain. Nobody's combinations are the same.

My 388 likes the APD tapered 2" spacer but I haven't done an ABA on the same day test to verify how much.

I doubt you'll see much difference using spacers. IMO your carb is way to large. That engine and head shouldn't require anything larger than a 950 carb.

I'd be inclined to use a 4-hole or Super Sucker, maybe even 2"' with that big carb, to enhance the booster signal, as much for more consistent mixture control, as anything.

If you're using a 4150 to 4500 adapter you already have a 2" spacer on it I doubt you need more.

I've noticed very little changes trying different spacers/none. I usually use a 2" spacer for the ease of swapping it with a plate throttle stop for the rare times we 90 race.