Gearcase drive indexing

"Hello all!
I recently obta

"Hello all!
I recently obtained a Merc Mariner MagnumII 150 h.p. Could anyone please help me figure out the year? Serial # OB291769 ?
My main question is this - I removed the lower gearcase to inspect the water pump impellor, etc - -and have rebuilt the water pump. I am now about to re-mate the lower unit, and am not sure of the small "forward-neutral-reverse" splined coupling indexing alignment now for putting it back together. There is no master spline, or specific marking that I can see. I should have marked it upon taking it apart, but didn't.
Does anyone have a manual that states how the indexing should go?
If not, I guess I'll have to go by trial and error after assembly, and running the motor. ARRGGHH!!

Thanks for any help!"

There is no indexing. This is

There is no indexing. This is generally disassembled when throttle/shifter is placed in forward gear. Try this: Place both lower unit and shifter into forward gear before reassembly.

"Hi Chad,i get 1988 US built"

"Hi Chad,i get 1988 US built"

"Kirk,
thanks for the info!

"Kirk,
thanks for the info! Oddly enough, that is how I disassembled it ( in forward gear )

Ian,
Thanks, also -- I went to marineparts.com, and thought that's what it might be!"