Do you happen to have a GMC frame and a Chevrolet radiator support? That would cause your exact issue.
I have that combination on the truck which I am building. The GMC crossmember sits 1 1/2" lower than the Chevrolet crossmember. I made a 1 1/2'" spacer to account for this.


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