[vettestr]

Stumble or miss only at cruise or light throttle >>

I bet this is a lean condition stumble. I would ask for all the basic/normal stuff to be checked .... float level, manifold vac. OK or no leak, timing at this RPM?, total timing.

Will it clear up if you add a bit more throttle ? It's a hot rod so add more timing and fatten her up a little more, increase RPM or get on the smooth side of the cam. Drive faster !!!