Up until the last part, where I had to insert the tip of the spline shaft into the pilot bearing, the installation of my new ACT Prolite Flywheel, and clutch system was pretty much complete. right then I spun the drive shaft and checked if everything was still working, and it was. The task was much more difficult than expected. I got help from my grandfather who is a retired mechcanic. He inserted the bolts on the bottom and left them pretty loose. Then we tilted the engine which looked like it had fallen into a groove and stuck, beeing though it didn't move back. We bolted it in and tried to crank.
Didn't turn, checking....tried again and still no turn over. We decided to pull the gas pump fuse, throw it in 4th gear, to see if it was the transmission, they didn't turn.

What could it be?

Help!

 

Did you force it at all? Maybe the spline seized somehow or maybe there is something blocking the flywheel.