a 1933 master wheelbase is 110" and a 34 master is 112" wheelbase .
A 1934 Chevrolet standard is 107" wheelbase.
So you have to assume the modifier of the frame put the mustang 2 cross member in the correct location and measure from there.
Looking at the side area of the frame where it curls up over the rear end. It appears that there is a low area stamped into the side. I have never seen this before .
Because all the stock cross members except the rear, have been removed, very difficult to identify it other than wheelbase.
mike