Then just have to change a logic jumper in the board, nearly the 040
The jumper is the leftmost of the 5 resistors bottom of this pic? (That's from BPPC with 060, so if 040 has the jumper in the other position that should be it. The other 4 resistors are the PPC PLL multiplier)
EDIT: Apparently this is not the jumper. If someone has a clue what this one (the leftmost) is, post a reply.
