Changing out drive shaft in my new gearcase...need help

Hello all...newb here.
I just received my brand new M2 (Magnum 2) gearcase for my 200hp H.O. Etec...man this thing is beefy. The seller pulled the drive shaft and shift rod out of it for shipping purposes. In the photos you will see a cut down drive shaft and shift rod installed...he did this to keep debris from entering the open shafts while in shipping. The cut down drive shaft is free floating and can easily be pulled right out while the shift shaft is screwed in. My questions:
The seller said I would not need to remove the drive shaft bearing housing at all and that I will simply pull the cut down drive shaft out and slip the 25" shaft in making sure to lineup the splines; he said I will feel the upper shaft lock into place with the lower shaft and I would not compromise the seal when removing the old and installing the new shaft. The problem is when I look in my manual under drive shaft removal and installation there is talk about bearing pullers....a roll pin and a retainer which hold the upper shaft to the lower shaft and lock it in place. The manual makes it look like a much bigger job than I expected.
What to do?

any advice?

You are right, there is a retainer internal to the works of the gearcase. When disassembling the gearcase, Evinrude has a special tool to pull the driveshaft out. This bends the spring steel retainer and allows the DS to be removed.
Since the gearcase is being disassembled anyway, the repair procedure will be to fix that retainer.

However!!! It is common practice to yank that driveshaft out and slide the new length one right back in. It is a practice that comes from the racer guys who might need to change driveshafts very quickly in the field.

I have done it myself, and I see no real problem with it, except the DS will come out easily if the gearcase is off.

Once installed....no problem.

The shift rod threads out, thread the new one in, set the proper height, and install LU.