That sounds like a deathmatch situation. Maybe if it were a really big tank with lots of cover; otherwise, whichever one gets a growth advantage will probably murder the other one.
yes.. for 3 days.. muskie/pike grows about 1mm a day at that size and are capable of swallowing pray atleast 65 percent of their body weight.. I have never kept muskie so wait for more experienced people to answer but they are very aggressive and predatory fish..