RE: Douglas DC-7
John,
A few years ago I built and flew a 1/16 scale DC-6 which flew fine. The airfoil was copied from the Royal DC-3 scaled up a bit and the tail section was symmetrical. Wing incidence was +3 degrees and tail was set at 0 degrees. Engine nacelles were all at 0 degrees. CG was 25% and seemed about right. I didn't have any problems with pitch and I'm wondering what could be causing your problem.
Hope you get it all sorted as I would like to build a larger DC-6 or -7 perhaps at your 1/10 scale. Please post some photos!
Paul