Hey, I’ve got a 1986 MCSS with the 305. I put a comp cams mild cam, performer air gap intake(spreadbore), long tube headers, pertronix coil and ignition module. Still have the stock 200R4 trans. I’m changing the distributor to the vacuum style HEI. Now I need to change the carb. I have the Qjet style intake already so I guess I need a spread bore carb. I ve heard that 600-700 cfm will do, but aren’t the Qjets 750-800 stock. What do I need? Thanks. Steve.
I also removed all the smog stuff.

 

The Q-J has air-valves on the secondary bores that control airflow at high RPM so there's no issue with over-carburation.
A really good book you may want to reference is How to Rebuild & Modify Quadrajet Carburetors by Cliff Ruggles:
Since you got an air-gap manifold, you may want to consider a Holley Sniper EFI Quadrajet. There's a YouTube channel called Uncle Tony’s Garage where there's a video about the pros and cons of doing this upgrade:

 

Hey thanks. Another question. If I go with the older style vacuum Hei distributor and use an old style carb. Can I get rid of things like O2 sensors those various sensor trees, knock sensor etc. I do need to keep the ecm for the trans(200R4) correct? What else does the ecm control?

 

Yes.
I'm afraid I don't have an answer for you on that. Engine control modules, body control modules, etc., are outside my wheelhouse.

 

ok cool, I think the ecm does run the trans but I don’t know what else. Have a good day!