So quick update following Rockingham.
Good day in terms of track time but organisation wasnt' the best - the website kept crashing so rang the office who didn't manage to get any conf details emailed to me as there were "only 2 of them in the office" despite me booking at 9:30 am friday. So I turn up at 8am Bank Holiday monday for the 8:30 drivers brief for 9am track time as she told me on the phone, which as it was bank holiday turned out to actually be 9:30 drivers breif with 10am track start, but still...
GTR was going well but feeling decidedly loose, loads of oversteer everywhere and nothing like it felt at Bedford which was a bit odd. Tried palying with tyre pressures and suspension but no Joy. Also suffered more breathing issues with it eventually chucking so much oil out through the catch tank that it was all over the front tyre and up the side of the car...

So clearly as well as being loose I was suddenly finding oil on the right front as i'm on the banking and heading towards the wall... hmmm
Had a good blast and dad got to drive it at last so good fun nonetheless.
Took it to get the allignement (hardly needed adjustment despite me lifting the front ride height a bit) checked and noticed the rear 888s were decidedly slick (i may have checked and adjusted the pressures about 6 times on the day but I didn't think to look at tread wear...doh!!) So a new set of 888s is currently en route from Demon Tweeks (they know how to charge for those bad boys now too, bring back the TA discount!!)
My concerns about the engine having to come out (again) and a set of rings being required were unfounded as a Leakdown and compression test showed all was OK so i put the gallon of petrol and box of swan vesta's away.....!!!
Have also discovered that the breathing issue may actually be casued by my baffling the the breather tank further following it spitting oil out at bedford!! So have put 2 breather hoses on now (previously linked the heads into one) and they are currently ending in a coke bottle - full boost on the road and no oil at all so looking promising but need to get it on track again to see if the tanks baffles are casuing it. May also need to put an oil drain from the head to sump too but hopefully that can wait...
The test run for the breathers also revealed missing on high boost (cold night) so lobbed a new set of plugs at it too, fingers crossed on that one.
Also got a new (used) speedo drive from MGT so hopefully I'll have the 4wd working properly soon as that's been really pissing me off. Thought it was speedo end so bought a new cable but turns out the gear on the drive was worn too so the cable alone didn't solve the problem.
So, now about to search for another trackday to see what happens next....