Stuck in forward after installing stern drive

1988 merc 3.0 with alpha one stern drive.
Bought this boat as project with new motor set in place but nothing hooked up and stern drive not installed.
I finally bought the throttle and shift brackets and installed them and every thing seemed to shift very smooth except I noticed shifting from forward to reverse the interupt switch would not return to the center position. The roller would ride up on the edge like it is suppose to do but would stay there until you moved the shifter back to neutral or forward. I thought since the stern drive is not on the boat I should get that on there and try to fine tune the shifting cables.
I put a new water pump and housing in the stern drive and installed the stern drive back on the boat today. Shifter was in forward and the shift shaft was straight and everything lined up real good. The stern drive slid all the way in very smooth till about one inch was left. The last inch went in smooth but it took some effort ( lots of muscle ).
When all 6 bolts were torqued I tried the shifter and it would not come out of forward. The shifter would move to about half way to neutral and then stop.
When un-hooking the lower shift cable on the valve cover going to the stern drive, the shifter moved fine and easy.
The boat has not been used since 1997 and I'm sure the cables are not new but they do move very freely ( or at least till I put the stern drive on )

Could the lower cable be bad or did I screw something up installing the stern drive???? Thanks in advance for your advice.. Russ

Re: Stuck in forward after installing stern drive

Edit:
Just reread your post. Sounds like you didn't install the drive properly. Did you have the shifter and the drive in forward when you put the drive on?
Sure hope you installed a new ujoint bellows. If not, put a new one on when you change the cable. Along with a new shift cable bellows.

Here is a link to the Mercruiser service manual. It will explain (with pictures) how to install and adjust the linkage properly.

http://www.boatfix.com/merc/Servmanl/6/6covr3.pdf

Re: Stuck in forward after installing stern drive

Thank you Don S,
I did have the shifter and drive in forward when installing the drive. i even pulled the drive back off it to double check. Both times it went back on easily untill the last inch or so which took some extra force, that is why I am wondering if I bound the cable in some way. Is it normal to use a little extra force to get the last inch of the drive on?? Is this a sign of a bad cable?? It did surprise me but all the bellows looked and felt to be in very good shape. I also took your advice and ordered service manuals #6 and #10, should be here this coming week I hope. thanks... Russ

Re: Stuck in forward after installing stern drive

when new motor was installed was the engine alignmment checked/adjusted? this could account for the tightness.the roller on the interupt switch should not be moving at all without a drive. if it does it could be in need of a new cable.the interupter should only work coming out of gear when the prop is under a load.