Even though they're heavy, I recommend buying or fabbing a G-Force style crossmember under an A-body... it allows you to tuck the exhaust up a lot higher than a stock or tubular style crossmember.
http://www.crossmembers.com/a-body.htm
Normally when you look at the side of an A-body with larger diameter exhaust you see the exhaust dipping down past the frame where it has to go under the transmission crossmember. This was always the lowest part on my Chevelle. With the G-Force style crossmembers you can have 3" exhaust tubing even with the bottom of the frame. Makes a huge difference in ground clearance especially with lowered cars.
As far as the moved mount location on the T-56... assuming you have a C-section (standard coupe) frame, just slide the crossmember back where it needs to be and drill 4 new holes in the frame.