If your 318 cannot initiate a spin,on the 2bbl, then, IMO, a 4bbl is almost a waste of time and money.
And the reason is; The secondaries may not begin to open until about 3000 rpm, and with 2.76s this is about 30 mph. I said begin to open. So at 3000, you might expect 4 hp. Count 'em . And the absolute most that 4 bbl will make, on your 73/318 is maybe 12hp@maybe 3800rpm/38mph.
In the meantime, the bigger primaries will reduce you throttle response and probably your fuel economy too; in all but steady-state cruising..
About the only place the 4 bbl might be a boon is when passing at 60 mph, and on the 3-2 kickdown, where the rpm might rise to about 3330. With the secondaries fully open, they might be worth 18 ftlbs or 11.4 hp.
Like I said..... with 2.76s.
The only thing that changes with a different rear gear is the mphs.
Ok, but say you manage to figure out a way to fully open the secondaries without; a huge bog, stumble, or hesitation, at 2500. Lessee, that might be 12 ftlbs or 5.7 hp.............. at 27mph.
Your results may vary.... but I doubt by much.
On the other hand, I once put a complete 318 top end and cam, onto an early 340 short-block, and it was a real terror in a 65 Valiant wagon with just fenderwell headers, and also with 2.7s, and yes with the 2bbl.
Ok "terror" to me, as it was waaaay too powerful for the chassis, and at age 22 it was also a handful for me, lol.
The only difference between that 340 and your 318 then, would be 22 cubes and probably close to 3 full points of compression.
So, IMO, for what you stated in post #1,
get your heads shaved and bump up the compression. That will be money much better spent.
