Ooopbs should have been sterndrive lower unit

Hi All I'm new here and it

Hi All I'm new here and it sounds like you all know your stuff.
Any how I have a 1977 470 w/ I think is an alpha 1 ( square top with lift ring) Had to replace the water pump and now the lower unit won't slide on all the way. it gets to about 1/2 " and then feels like it hits something. Must I have it in foward and how do I tell if the lower unit is in forward?

"Yes, the control box in full

"Yes, the control box in full fwd, the splined shaft in the lower unit turned fully clockwise untill the prop locks counterclockwise(try not to move the prop or it will go into neutral.)raise lower unit, insert copper tube into plastic guide,raise unit ,if shaft does not line up turn prop counterclockwise to turn driveshaft backwards a LITTLE BIT.you`ll feel it drop in.
install lower shift shoe on splined shaft(if it`s straight ,that fwd, raise unit,install foward most nut only enough to catch 2 threads, make sure the shift shoes mate up, install 2 side nuts and tighten those fisrt, then the rest.
http://www.boatfix.com/merc/Servmanl/6/6covr3.pdf"

Ok thanks for the info I will

Ok thanks for the info I will try to get to it doday thanks again.