I never have swaped out a lower unit before but want to put the stock B1X back on for some prop numbers. Is there anything that I should know about changing it? I am thinking it is straight forward....rmove bolts, collect drive oil, remove lower and same steps in reverse to re-connect new and add drive fluid?

It is very easy and straight forward. I would get a new upper to lower gasket kit. I never really mess with drive internals, but have separated an upper and lower to install a larger spacer. It was simple. There is bolt below the plastic cap on the back of the drive that can be missed if you don't know its there.

Actually that bolt under the plastic/rubber cap is for the trim anode. You take that off and under it, is a 5/8" bolt head that holds the uppers and lowers together. That would be going from B1 to Imco. With the Imco, that bolt is eliminated and so is the trim tab anode. It would be a good idea to add it. Is a 7/16" bolt, with the 5/8" head.. The bolt that holds the trim tab anode has a 1/2" head on it. And it comes with a new anode, along with the star washer.
Dick