I did remove both P-mags from both of my engines for the installation. I also removed the oil filter because I had the angled adapter for it.
This was done just to give me a little more room to move the engine around. I was working alone and didn't want to risk scratching the mount.
The P-mags are significantly smaller than a standard mag, so you may want to remove your regular mags.
Not a big deal and you will want to check their timing before firing up the engine anyway.
Good luck mounting your engine, that is a BIG milestone!
BTW, follow the
Illustrated Guide to Engine Hanging instructions on this site and you won’t have any problems. It took me exactly 45 minutes to install my engine, working by myself, following those instructions, and without a scratch.