Justice,
As a hopeful help to go along with Mike B's suggestion to get the tape measure out and start checking your frame and wheel base measurements, you can compare your measurements to the charts in this GM Heritage Center resource document
1949 Chevrolet Truck Data.
You will find the different wheel base and frame measurements for the many different models in the early section of the document that include drawings of the trucks with points of measurement for each model.
This doesn't address the possibility that you got a GMC frame instead of a Chevy. I found this long ago thread on the
GMC VS CHEVY that points out that among the difference, the front cross member/engine mount is farther forward on the GMC to allow for the slightly longer GMC I6's installation. If (?) you got a GMC frame and installed your Chevy engine (216/235/261) without changing the front cross member location, that possibly could account for your engine/transmission now sitting farther forward and no longer matching up with your rear axle/torque tube location.
Let us know what you figure out and we can try and provide more help.
Dan
