okay, here are the measurements: vertical distance from the center of the hub to the top of the forward rotisserie frame member is 31.5 inches. in the original blueprint that measurement is 34", but I lost a bit of height by mitering in my horizontal hub mount. If I had welded the mount on top of the vertical frame member, I'm closer to the blueprint spec, but I figured I was putting much smaller cars on this than the buick it was originally intended for. The width of the GTV about 6 inches back from the front edge, which is where it will cross the frame member, is less than 29" (the widest point is further back and won't interfere with anything). I should have about 3" of clearance at the closest point of potential interference. The rotisserie might not work for an american car without some extra height on the mast.
Taking PSK's comments, I will drill through and use a pin to secure the mounting framework to the hub. I don't trust just the friction of the 4 bolts, although they will let me get the height exact before I drill. hopefully a '67 and '71 GTV have the same centers of rotation so the hole works for both.
Stan Swanson, Eerie Erie, Colorado, '67 GTV (daily driver), '71 GTV (Kyle's), '91 164 (snow car), '56 Lotus 11(gone to Oz), '59 Cadillac M+M Hearse, '74 MGB