Cheers for the offer. As of last time out at Wroo I think I have it sorted. The thing managed a 55.0 short circuit on tyres so old they had sparks coming off them.
The solution is to vent the blow by via a path that doesnt go through the back of the head. I think the most of the rest of it is bollocks - eg the Mines head baffles, tiny (<1.0mm) oil restrictors. Ofcourse venting the blowby is really just a bandaid, albeit a common one. It shouldnt happen in the first place but a relatively small amount of blowby appears to cause big probems in the RB's. There are no end of RB26 out there who have this issue but it isnt a problem as they are only driven on roads where it doesnt show up.
There is another discussion to be had about ring thickness, tension and selection - eg what forged pistons can I run and use Nissan rings?