my experience of this in repect of YB heads is limited to having listened to the views of those who have done it before and then having had the head and the block skimmed to ensure good results. i was fortunate in having the engine out in both cases.

HOWEVER..

many pro's recommend the WRC gasket over the cometic one but pro's WOULD cos they can sell you them, and if they fitted the (cheaper) cometic one for you and you had a problem then you'd blame them for fitting a cheaper gasket, whereas if the WRC one failed they'd find a different excuse.

I know of 2 respected tuners who frequent this board who have not had any problems with cometic gaskets (neither have i either) and they would say that the typically disgruntled cometic users had been looking to save money so might not have had the head or block (or either) skimmed, on the assumption that it was ok, but then suffered failure cos it wasn't!

someone with the funds to use an expensive WRC one might also have had the whole engine stripped and rebuilt and deemed the cost of the extra for the gasket to be justified in this light. after use on the engine with repeated heating/ cooling cycles and then subsequent dismantling, the most likely component to require refacing is the head.

if you need to check the block because the engine is still in the car proceed as follows:

clean the top of the block with 120ish wet and dry ensuring no crap gets into the bores and wipe the surface with thinners / degreaser.

go to RS components or elsewhere and buy a pack of shim stock. use the thinnest - usually about 1 thou and stick a piece on each end of the block.

cover the head face with engineers blue and sit it on a strip of shim at each end and see if the blue shows on the block face. if it does then take the engine out and skim the block to fit cometic, or try the std gasket! if it does not touch you're ok.

you can also do this with standard kitchin ally foil which is usually under 1 thou thick. if the blue does not touch with this then the head is perfect.

alternatively, get a piece of standard photocopier paper 80gsm. this is usually about 2-3 thou thick uncompressed but when you soak it in water it will compress to less under the weight of the head.

Note: only the best engineering shops can machine a head to within half a thou despite what they tell you.

if the block is fine then definately use cometic - if not then maybe the std one will last but i've no experience of one of them lasting they've always failed on me!