Gear Housing Installation

[quick_claude]

Please help. I replaced the seawater pickup impeller on my '79 MerCruiser 120hp I/O. BUT, now I can not get my I-Drive gear housing to tighten back up to the drive shaft housing. I can get it close to the point where the water inlet tube is in the water tube guide and the lower and upper shift shaft is together. I made sure the lower shift shaft is full clockwise (forward)and upper shift shaft is full forward (straight ahead). I turned the prop counterclockwise to hold the gear housing unit in forward gear. But I hit resistance and am afraid to force the issue. I am afraid that I will damage the splines on the drive shaft assembly. I come within about an inch of coupling the two units but no cigar. Any hints or suggestions would be very appreciated. THANKS!