Morning Paul, Heritage sell the SCAT one's for about £10.00 These just need the rocker covers drilling and the fittings putting in and tighten the nut up on the inside. You can fit fancey breather towers/ collection pots or just run the pipes from these slightly up and then back down to the bottom of the gearbox level, so they just vent to air. My Hi-reving type 4 engine, has the rocker vents but I have not fitted any pipes to them. It also has a vent pipe near the dizzy which I have put a short pipe on, mainly to keep the rain out
Rob