4 hole spacer ona single plane

I was only using the RPM as an example. Not recommending it for your here. You shift too high for it and I'd stay single plane. In terms of what you have on hand... I'd say the Street Dominator would be the best single plane compromise bcause it's got less plenum and runner volume. But the M1 I think will make more power where you need it. I'd also baseline without them but I'd try a 1" open spacer on both to see if they pick up. I'd also make sure the intakes are port matched to the heads. RPMs making 280cfm is not as easy as some think.