I'm legit again, my "new" '68 LB

['68OrangeSunshine]

I may get flamed for saying this, but I've never had luck with any Rochester carbs. I've given Holleys a few tries, but finally settled on the Carter AFB design, which is now only sold by Edelbrock. I have a Carter [Federal Mogul] 9635S [= Edl 1405] manual choke 600 CFM 4-Bbl on my V8 350 in the '71 GMC Jimmy, and an Edl 1404 manual choke 500 CFM 4-Bbl on an Offy intake on an L6 292 in my '68 Chevy C/10 Stepside.
If you still have the original OEM Quadrajet on your 307, then get it rebuilt by a professional. I have found Q-Jets to be finnicky, and each one was apparently hand-matched to the original engine when first sold. You can't get a generic replacement carb from the auto parts store, and turn in your old Q-Jet as a core -- you'll only get junk back. I've made that mistake. Then I put a 780 CFM Holley doublepumper on the Jimmy's engine and it sucked 2 valves, running on 105 octane. Replaced the engine with a crate 350 and a new Carter AFB [1999] and that set up has been running good in the Jimmy ever since.
Rebuilt a fresh 292 for the '68 Stepside in 1977. In '78 I upgraded to a 390 CFM Holley, Offenhauser intake and Clifford headers on the bored-out [.030] 292. Ran for 250,000 miles -- took me 25 years. Downed the rig for overhaul in 2002. In 2005, I was back on the road with another fresh 292 rebuild [former Original Engine] The Clifford headers and Offy intake, cleaned up nice, and went on again. For the 500 mile break-in period, I had the Holley, then a bad backfire knocked out the power valve, and we found we could'nt get it to set up right anymore. Suspected warpage of throttle-plane. It was cheaper to get a new Edelbrock 500 CFM to replace the 390 Holley. Still running good 16 years later.