Installing an Oil Catch Can
A couple posts below that, DrLoch linked to some check valves also. That would be easier, you wouldn't have to modify them.
I found this for a PCV, doesn't give dimensions but it might work without the labor of grinding ect.
Toyota Supra Twin Turbo Car Truck Factory Genuine PCV Valve MKIV | eBay
Toyota Supra Twin Turbo Car Truck Factory Genuine PCV Valve MKIV | eBay
Not the UK, but Hungary! Or Brazil for the flex fuel veriation, According to this!
https://en.m.wikipedia.org/wiki/GM_Family_1_engine
https://en.m.wikipedia.org/wiki/GM_Family_1_engine


