OK, so I just fitted the engine cover back onto the car to double check if it will fit with the 17mm plenum spacer. When I fitted the spacer and the cover I thought it was hitting the bonnet so took it back off. Ive been thinking about it during the week and for some reason really wanted the cover back on
I put a nice smear of Vicks vapour rub on the 6 bulges of the cover, then closed the bonnet and started engine and gave it a few good revs. When I lifted the bonnet I found NO Vicks on the bonnet lining. So I am now going to make up some play dough and put a 3-5mm layer on the engine cover and try that. I do this when building my Valiant engines to check piston to valve clearance with a BIG lift cam. This way I can cut it and get a cross section of the play dough to see exactly how much clearance there is.
And I also pulled out the rubber grommets in the cover and turned them upside down, this sat the cover about 2 mm lower.