Definately an auto. I broke my T56 on the Power Tour 2 years ago. The 4th gear syncro key had been damaged. They were $6. I decided to swap the 3/4 aluminum shift fork for a steel one, replaced the 4th gear syncro, and some other misc parts. I spent $200 for parts & an evening repairing it.
The parts are way cheaper & the only special tool you need are a press. This tranny took 10 years of abuse behind my big block before breaking.