Another problem for you other than the pan you use is the engine/trans inclination angle showing in the photos...which my experience and eyeball judgment estimates to be somewher
e around 5 degrees. You should be positioning your engine and trans to acheive no more than 3.5 degress of inclination angle if you expect to achieve satisfactory U-joint working angles. The front of your engine is too high to be able to acheive that without cutting the floor to raise your transmission up in the rear. You can achieve that low of an angle in a 1st-gen LS swap T56 combo without cutting the floor only if you get the front of the motor low by using custom engine mounts and a pan with a front end profile no taller than a stock F-body pan or by notching the front crossmember to clear the pan of your choice. When the correct angle is acheived, the rear case of the T56 will barely extend below the subframe.