I am surprised that you aren't having problems with your clutch/brake/accelerator pedals interfering with your toe board.
Before you raise the rear of the cab, you will need to check the gap at the front mounts as mentioned by Dusty53.
I would also recommend removing the 2 bolts which hold the bottom of the radiator support to the front crossmember so that you don't put undue stress on the front clip (fenders, radiator support) while you jack up the rear of the cab.
The reason that you need to do all of this extra stuff is because cab adjustments are normally made before the front clip is installed.
Carl

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