[Barry_R]

Compression is a bit light for that cam in a "real" 427. It'd be stronger through the midrange with either a shorter duration stick of some more squeeze. I normally run a 254ish deal on the street at 482 cubes for a peak around 6200-6500.

The 750 cfm carbs are perfectly fine. If they are vacuum secondary they will run like a 750 double pumper until the primary airflow is sufficient to open the rears up.

The big plenum intake is pretty huge - I suspect that many of the responders have never laid hands - if even eyes - upon one. Adding two inch spacers makes a big plenum even bigger and will theoretically move the tuning window up into the stratosphere. Might not be the whole deal but certainly a contributor.

Why would you need the spacers? I've run several of these and never needed a spacer unless you're trying to run the carbs in the normal "front to back" orientation or trying the run a 4150 style secondary metering block instead of a 4160 type plate. Both of those are good pure race modifications but really unnecessary for any sort of street build.