Found a single carb tunnel ram in back of shop. My present combo is 408 with M1, 750 Holley, R/T head with mods, .557 Mopar cam, 8" converter/ 4.30 gear. Turns 10.50's-60's/124 in good air. Will I get anything extra with the swap?

I'll go out on a limb and say...NO WAY. Rather, no way I'd run a conventional cast tunnelram with a single 4. The distribution is awful! Now put another holley on the TR and it'll likely pick-up a tenth or so depending on the model.

The only way i would use one would be with direct port injection of some sort and a good flowing throttle body. Then match the cam and converter to that manifolds rpm window, and maybe work on the runner sizes if they are small for your motor/head combo.

Over the weekend, I found the dual quad top and what I think are the correct Holleys with the vacuum secondaries.

A much better option. My thoughts are how are vacuum secondary carbs going to function when they have a lot of flow capacity to cubic inch. Maybe a call to Holley tech might help, or someone may have done some research on a dyno to give you a starting point. How big are the carbs?

You need to tie the two vacuum pods together when using them on a tunnel ram take