Pre-cut...
each of the three packings on a one inch diameter alternative as space at the shaft log is minimal. Cut through an overlapped material at a 45* angle to get a better end seal.
It's a challenge to do with the boat in the water. Be prepared for a gusher!
Be sure you get all the old packing material out of the log before starting to install the new. There is a tool for that, but something with a sharp point and long enough will do (bent fishhook, etc.).
Space the cuts at 4, 8 & 12 o'clock around the shaft when installing the packing. Tighten firmly by hand to stem the flow to barely a drip then fire up the engine and put her in gear to seat the seals and make any tightening adjustment as needed.
Don't forget to tighten the lock ring down solidly when through.