I would like some more information about splitting cases as well. I am thinking of starting a thread over in general discussion focused on the P6/P4 so we folk can get some more advice and help, and keep it out of buy + sell.
There is a post in the Lovers of Minarelli V1 group on facebook that was of some NOS Minarelli tools, that apparently were for the P6 engine. Some folks were commenting and suggesting that you need these case splitters otherwise you crack the cases. I'm sure it's been done without them, and I would like to hear how. I know Chad Burke has the NOS tools at his shop in Michigan for working on these engines, and I may end up taking it to him for a rebuilt, but I definitely want to try and get some more information. I am going to actually start that thread now and I'll link you guys to it shortly.
Brandon Weiss (mopedallday) has a P4 and a P6 engine, I believe he said he has never split the cases on them but he may know more about doing it.