Separated SSM3 drive in order to change oil hose ....found out really quick that was the easy part.
trying now (what seems forever) to marry up the shaft into the transmissions?...harder than trying to
thread a wet noodle!

It can be challenging, or just slip right in. I use a couple of screwdrivers to manipulate the yoke into the correct alignment. If you find yourself getting frustrated, walk away for a bit and come back later.

If you still can't slip it in, try some candles, Barry White and wine.

on my old scarab with TRS i found if i took a packing string and ran it through the u-joint area next to the shaft that goes into the trans, i could pull it up/down enough to help get it aligned...the drive would go in and then i would just pull it back out a hair to pull the string out.
I even tried using the paper masking tape to help keep the u-joint/shaft from flopping around.....figured one cycle of up/down would break the tape and on away we go That tape trick only worked once...i think it was a fluke....but the string thing worked quite often

Oh it also sometimes helps to twist the prop shaft as your trying to marry them up as well...

tying the string to the shaft sounds like a good way to go...I'll try that.

Also, what's a better placement for the large o-ring when marrying the drive to bell housing...........placing it in the round slotted female grove of the bell housing -or - around the male end of the drive above the u-joint?

I don't remember an o-ring to be honest...its been 20yrs now that i haven't had my old boat...but if there was an o-ring there, id keep it on the drive. If you install it into the bell housing you cant guarantee the drive will go in straight and not push the o-ring out...

There is a place in the manual that says to glue it to the helmet prior to installation. I lube it and slide it onto the drive.

Masking tape (clean out after ya run the boat) definitely leave rubber o ring on drive, wiggle prop shaft. All make life a little easier another set of hands are helpful.