47-55.1 Rear Cab Mounting

[fauXGT]

Working on the Rusto-Mod, and with all the different parts from different trucks, I can't find the info I'm looking for.
It's a 3100 frame in almost perfect condition. The cab is from an old farm truck. A 6400. The cab had a few minor rust issues, like most, but the rear cab mounts were in great condition. They don't line up. 3100 frame has offset holes to the frame and the cab shackle mounts are straight up and down.
All the info I get from searching is 3100/3600 frame to 3100/3600 swing mount measurements as far as length from bottom of shackle to bottom of frame. With equal space on the rear of the cab as it wraps around the frame, (1.5") from above and sides to the frame, it gives it a slight rake. .6" higher at the rear of the cab compared to the front to the running boards.
Does the cab run parallel to the running boards or does it rake a bit like a hotrod?

Any help is appreciated.
Chip