Help, with a friends 67 Cuda 340 issue

Hey guys, wondering if anyone may have a idea about a issue with a car.

My friend has a 67 Cuda, with a 340, Auto, 600CFM Holley, Torker 340 manifold, headers and points ignition.

I have ridden in the car when it is running good, and its a street terror.

Problem history and symptoms.

A few weeks ago he was at a show, and it started to rain. At the end of the day, he started it and let it idle, with two other cars and talked to his buddies.

They left and he found that his engine had died. He tried starting it and it wouldnt start, but cranked ok. After looking at a few things he found a cracked dist. cap. He replaced it and tried starting it.

He said it bucked and spit fuel and backfired etc, another bad cap, replaced and it ran, but wasnt right.

He got home and replaced the points and tuned it, he said it still kinda surged at midrange and was down on power.

I went over to help yesterday, since he had a old Holley (1980 vintage) and said it had backfied we replaced the power valve, replaced and gapped the points.

The float bowl was clean inside and the jets had nothing in them. we drove it again, and it still was down on power and had a slight surge midrange.

I drove it, never having driven it before, it idles fine, but if you get on it around 30mph, it is a dog no power, and it does have a slight surge at a steady 40 mph or so.

We checked the vacume advance, it seems to be working, we timed it at about 10 before, we replaced the distributer and points etc and i drove it again, same issue, no power at midrange.

This car can normally chirp the tires manually shifting from 1st to second and kicked my 440's butt from a stop before, now its just falling on its face.

Any ideas, could it be the carb itself? It seems ok, no belching of black smoke and it seems to be tuned ok.