I'm ready to install the new 1-piece shower stall into the framed-in location
in an existing bathroom. The ABS piping, including p-trap, is installed with
the exception of the vertical pipe between the p-trap and the drain.

I'm having cart-before-the-horse confusion, at this step.

The drain is, basically, a 2-piece assembly, with the drain to be installed
from the top side of the shower stall floor and a large washer and nut to go
on from underneath the stall floor to hold the drain assembly in place.

Option #1:
If I attach the drain assembly to the shower stall prior to putting the stall
in place, this means that the ABS drain pipe needs to be installed prior to
this, and aligned perfectly. In my mind I see a vertical pipe coming up from
the p-Trap onto which I'll have to precisely aim the drain hole, while
manhandling the very cumbersome shower stall, all the while trying to mate
the pipe and drain and not snap off the pipe or mangle the seal on the inside
of the drain assembly.

Option #2:
I could place the drain's washer and nut underneath before installing the
shower stall. Then after the stall is in place, I could install the drain
assembly from above and try to attach the washer and nut from below. This is
not an optimal scenario due to the limited access to the nut (basically, just
fingertip room in there).

Option #3:
Install complete drain assembly onto the shower stall floor. Cut to length
the ABS drain pipe between the drain and the p-trap. Install the shower stall
with drain in place, and with the ABS pipe loosely attached to the bottom of
the drain (it's a rubber seal connection, not a glue-type). Then, from below,
glue the pipe into the p-trap. There's limited room for this, but slightly
better access than there is to the nut (option #2, above).

Which way would you attach the drain? Other ideas?

Thanks,
Sparky