Pulley-mounted crank trigger w/stock Magnum EFI - trigger notches?

Sure you could. Your machining would have to be top notch (pun intended) and you could even use the stock crank sensor to generate the signal. The window size will have to be the correct size relative to the diameter of the wheel, which will be different from the oem magnum flexplate but with some math you should be able figure it all out. Good luck.