Tightening cam nut without the proper tool
 

My build is being held up by not being able to source a damn P237 cam holding tool. Was toying with idea of using the chains / flywheel lock to react the torque. Now I know you'll all instantly say don't do it....but surely that timing chain can take it....no?

Probably not a good idea to tighten using the chain.
Stromski Racing has a special tool just for tightening the cam nut. It is however a bit pricey.
Rather than ordering the cam nut crowfoot and cam holder, I had a machine shop cut of the bottom 5/8'' of a 1 13/16'' 3/4" drive socket and welded a 2'' 1/2'' drive extension on the side.
To hold the cam, I cut off the box end of a 17mm combination wrench and welded about an 18'' pipe onto the open end stub. Now you can tighten the cam nut while holding the cam. It ain't "purddy" but it works.