I have a box of Hornady 17M2 ammo in my hand, and the label on the back reads; (and I'm going to type this)
1) To avoid serious injury from a ruptured cartridge, 17 Mach 2 ammunition should only be used in firearms with components specifically designed to safely fire 17 Mach 2 ammunition, including the firearm's action components (bolt/firing mechanism). Do not use this ammunition in firearms that have been modified unless ALL the action components have been specifically designed and verified by the firearm manufacturer as intended for 17 Mach 2.
THAT, and the fact that as recently as a week or so ago, someone was offering new Marlin bolt action 17M2 rifles for about $138, it seems like reworking a Cooey might very well be more trouble, money, and risk than it's worth. I realize the warning is a pretty standard one, but food for thought.