Check to be sure all the parts fit separately before assembly, like the pilot bushing to input shaft, and clutch disk to input shaft.
Be sure you have the clutch disk installed the right way.
Do not use the bolts to pull the transmission home. It must slide in by hand or something is wrong.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-