I put a M11 under my 37 but didn't cut the frame. I paid 75 dollars for all the A-arms, rack and pinon for a core to buy a new one, used the spindles and all. My welding friend plated the side of my original frame, welded in the cross member and sping towers etc. I put in new ball joints,shocks, and bought after market rotors with chev bolt pattern to fit the stang spindle. No problems so far and the hardest part was taking the stang parts off in the junk yard with it raining!! Been running Good for 6 years.
