I got a AL manifold with two Carter 4 BBL carbs. If I put this on my stock LG4, what will most likely happen?

Super Bog?

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1986 Black/Gold LG4 Z28
Original Owner, 200,000+ near trouble free miles.
Mostly Stock.

1995 Dark Red Metallic Corvette Coupe Original Owner

 

No power because the distributor won't get an advance signal. Once you put in a vacuum/mechanical advance distributor, it will do better.

Chevy put such a system on 265's and 283's, as well as bigger things. The 4 bbl's they used were small, though, around 400 CFM. What kind of Carters are these?

This has more visual appeal than performance potential, but it's a neat concept if you don't have to worry about emissions. To really make it work, you'd have to get better heads on it, a better cam in it, and better exhaust on it. You'll have a few "issues" to work out, like tranny TV cable (if auto). With some tuning, it could be an interesting runner.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 2.73 open. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, ported heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

I've seen 2 x Holley 390fm's on a 305 in CA last year. Sounded good and ran well but I didn't get a ride in it. It was prety severely modded, though.