try to locate a source where the oil enters the combustion chamber or exhaust port, i'd start with the crankcase breather. disconnect the hose that goes to the manifold / intake and see if anything changes about the smoke
if you let it idle and take the oil filler cap of, does the engine start to run different?
jup, something like that. if it starts to run different in any way it will mostlikely be pistonrings or breather related (let's hope for the last, that's the cheapest )
Thanks, I'll try that tomorrow. Another thing to note is I just drove 90 miles cross country and it hasn't lost any power/fuel economy. I'm hoping it's valve seals as they needed doing anyway (plus I can leave it for a bit, like the lazy cheap bastard I am )
i used two cans a few years ago on a hyundai that was burning 2litres of oil + a week and it stopped it completely. surprised it worked tbh, i would say its worth a go. the hyundai had compression problems due to worn rings.
we used some in the plug holes and turned it over to get excess out then put the rest in the oil. bit of smoke on start up and after about 300miles no more oil burning! couple of years later the engine is still working fine.
Fair enough, I'm never a big believer in aditives but might be worth it in this case as it doesn't appear to be rings.
So a little update, I did a due oil change today anyway and lifted the oil cap while running. No noticable change but it did spurt oil all over me a bit. I'm thinking probably valve seals or something similar.
Removing the breather pipe makes it rev all over the place I'll test that on a hot day when it appears to burn more.
But it's not at a rate that will hamper me cost-wise (top up every couple of weeks or so) 
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1988