You may encounter an issue with the surface of the frame where the top shock mount attaches on your '48 frame. I think that they are scalloped in the area where they go. I had that problem and also had trouble finding a point from which to measure to locate the bracket in the proper place and at the proper angle. The way I resolved it was to bolt the shock into the lower shock mount. Once it was tightened up, the shock pointed me in the right direction as to where to locate the top mount.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission