Merckick calibration tool......
 

We watched that in the shop last Friday and the immediate response from all was "if that phuckin Sally can do it than we sure as hell can"

Thanks red.....gonna try lipstick again....just to be sure...

I found it by measuring the engagement of the alignment tool and seeing it was short the same distance as the drive away from the bellhousing

If your drive is going in until the 6 bolts on the outside bell just start into the 6 holes on the drive your are hanging up on the gimbal bearing. Take a block of wood put it on the backside of the drive and hit it with a heavy hammer or mall,sounds crude but I have found over the years sometimes it's the only way. JOHN SR Just my 2 cents

I ruined a coupler this way lol

I ran into the same issue when I pulled a 496HO and put in a complete aftermarket 557. My problem was that I installed the flat fiber washer with the spring and turned out I had bought a motor with a later model bell housing. Didnt need the washers and after removing, everything lined right up. Good luck.

how are the splines on the drive? did u test fit a splined shaft into the coupling? what alignment tool do u have? i found the best one is an old splined shaft with a bar welded to the end of it

Devide and conquer. Take a motor-end yoke the same length as yours, or take yours off your drive and see if it will go into the coupler without the drive. Once the yoke goes in and out freely retry the whole drive. if you are sure it is not the yoke binding you can be sure the shifter is alligned.

I assume you know yokes come in many lengths. Some bell housings on the motor have the rear mounts in different position causing yokes not fit. Assume the yoke stops 1" before the bottom of the coupler, put a tape into the coupler and measure the length from the gasket to the bottom of the coupler. Then measure the u/j assy from the gasket surface of the drive. If the u/j is more than 1" from the depth in the coupler you may bottom out in the coupler. Feel the shaft of the yoke when it jams and feel how much splined area is left exposed at the coupler.

When a drive is jamed like this, press on the back and wiggle the drive to determine if th u-j section or something around the bell housing is draging.
God luck Buddy.