The breather mod is just bypassing the factory breather with a section of rubber fuel hose running up to the engine bay, zip tie it off somewhere (I use the coil bracket) and stuff a small filter in the end. I also put one loop of tubing (360' turn) in mine at the upper end. You'll want to leave...
Should be British Standard Pipe Taper (BSPT) 3/8"-19 TPI, but double check that.
Gearing Dynamics in your neck of the woods sells the correct PRV. I recall looking for another source years ago, didn't have much luck IIRC.
One option might be to tap the stock knuckle grease plug for a more...