My vote is to drill and tap the M8x1.25 knock sensor hole used on 2001 and up 2.5/3.0L engines to the M12x1.5 used on earlier models like your's. I would recommend against splicing the sensors. The calibration in the ECU to detect knock is specific to the sensor. By splicing in a different sensor you might possibly confuse the ECU. It could either not detect knock or detect knock where there is none.
Keep up the good work but please stuff some rags in those intake and exhaust ports before a screw falls in and puts a hole in your piston.
