Using the calcs - 7.77 equals a 12.31 in the quarter.
I had a 3000 pound '66 Chevelle with 5.13 gears, 29 inch tire, TH400, a garbage convertor that was at most 3000 stall. I can't lay my hands on my records from that car right now but if I remember correctly 1.40-1.45 60's were the norm. The car ran pretty consistent 12.05-12.10s, on the button with a 150 kit, the car would go 11.96-97. The problem I have here is this was an iron head 331 small block with a 780 vacuum carb, a Cam Dynamics solid cam and some cheap speedway headers. Torque was a joke. You have a bunch of cubes and massive torque in comparison so I have to question if the combo has gone off the rails somewhere? I know you said that you dropped some compression with the new heads but it almost sounds like smog motor territory. Maybe the 92/93 fuel is too much octane. Maybe the cam needs to be moved, I assume it is degreed to the card at this point. I don't think the carb is even close to the issue. Maybe the heads nees a cut?