Paul Gardner-Stephen reports that he’s been asked a bunch in the past how to change the drive numbers on the internal 3.5″ drive on the MEGA65. By default it sits on device 8 like the Commodore 64 and device 9 (for the optional 2nd 3.5″ drive via the little round PS/2 style plug on the MEGA65).
You can do this the old fasioned by setting them via the Open Command while in 64-Mode or the easier way in MEGA65 mode is to log into Freeze Menu (via long pressing the Restore key) and then press 8 to toggle the drive number of the first internal drive between 8 & 10 and 9 to goggle the second drive between 9 & 11.