Pull out the spindle and clean whatever grease you can, within reason.
Lay the bike on its side, with the fixed cup down.
You can now squirt the PO onto the shell threads and have it run into exactly where it needs to go.

BTW-
The crank bolts are 8X1.0MM, not the more common 8X1.25MM.
when I bought mine, I drove the guy at the auto parts store nuts until we figured out what was wrong.

Also-
Are you going to service this or just install a cartridge BB?
If the latter, look for a code on the spindle such as 3-P, 3-S etc.
That tells the length and we can suggest a "symmetric equivalent" cartridge BB.

If the races and spindle are good, buy 22 1/4" bearing balls and a tub of grease.