'71 C-10 Manual Transmission Swap

[Mr. Rex]

I own a 1971 C-10 2WD longbed with 250 6-cylinder engine, 3.73 ratio differential, and 235/75 R-15 tires. Forty years ago (when I was younger and had more energy than experience) I swapped out the 3-speed Saginaw for a 4-speed from a 1970 GMC donor truck. At the time, I thought it was an SM 465. During the past few years it has begun to howl and whine and I felt that it needed an overhaul. I pulled it out of the truck and after close examination discovered it was a 1953 SM420. Now I would like to replace it with a 5-speed transmission.

Modern Driveline, Caldwell, ID has recommended a T-5z Tremec transmission originally meant for the Ford Mustang, along with the necessary parts and adapters. Does anyone have experience with this setup and any problems that I need to anticipate? Any advice, pictures, or stories would at least give me some perspective on the task that awaits me.