302, bored .40 over
"step up from stock" cam
high-rise, dual plane (1500-6500rpm) intake
9.5:1 comp
351W heads, 60.8cc with 3-angle valve job
headers, most likely (getting there...)

I have a Holley 750 which i'd LIKE to use, it has reasonable jets in there now (70--also have some 66's i could put in). I've been told that i can use it with no problems (i.e. gaps) by putting a stiffer spring on the vacuum secondaries (in the vacuum diaphragm). I know that NORMALLY a 750 would be too much on a 302, but is it possible to adjust it to where i would get reasonable gas mileage/performance? Reasonable, in my opinion, being 15-20mpg with normal conservative driving.

My other option is a Holley 600cfm vac. secondary that i have laying around. It's missing the choke and some other minor pieces, but if there's no way to make the 750 work then i could use this.

So which one should i use? Is it worth making the 750 work, or am i just going to kill the engine with too much carb?