when tuning a performance engine, tune ignition first and then tune your carburetor. 4secondsflat has a website and offers a tuning book that is really easy to read and will teach you what to look for in a print medium. In the old days (1960's) a speed shop would use a distributor machine and...
Assuming not positraction, Jack up rear axle and block one wheel...put in gear, slowly increase speed to see if vibration occurs and repeat for other wheel. If posi, remove one wheel ,install lug nuts and repeat procedure to rule out tire problem.
I am by no means an authority on this subject but, our cars have some weaknesses in the electrical system... especially at the firewall connector, examine this point for corrosion and heat damage, the amp gauge is often by passed and there are articles showing how to do this...the instrument...
probably need about 370 rwh , a 3.91 gear and overdrive transmission with a 27 inch tall rear tire. Will take some time to tune ignition and carb to get drivability and mileage where you want it
try 20 to 22 degrees initial, then connect your vacuum advance to manifold vacuum and using your vacuum guage, adjust the idle mixture to the most rpm or highest vacuum...
talk to mike at MRL , probably the EQ la type head, should be a bolt on and flow much better than stock , not to mention the great design of the combustion chamber.
I bought them about 10 years ago and used them up until last year,, from the posts I read now they must have been re-calibrated...mine were very stiff and still had wheel hop....
You might benefit from some of the DEI or other brand of fuel line insulation in the entire engine compartment, from carb all the way around to the area of the firewall.
once you get the electrical figured out...sounds like your carbs are leaking gas into the manifold, I may be wrong but, weber carbs may like less fuel pressure than the factory setup....
I have the Dynomax welded stainless straight through mufflers and an H pipe on mine and they don't drone but are loud at 2700 or above. If I had it to do over would go with magnaflow...