I have measured my Pace RC31 forks against a pair of 29er rigid forks (Bontrager) and they appear to be exactly the same.

Could I use the Pace forks on my Rig? Please help.

Worth a go – why don’t you just see if the wheel fits? I’ve got the 440mm version of the RC31 and there would appear to be loads of room. And I’ve ridden on Cannock Chase with someone running a 69er with an RC31 up front. As your rig is already a 29er it should be spot-on, and much more fun than the Reba it came with IMO.