Engine cover bolts

Just removed my TF engine cover and people say 10x10mm bolts yet I have 12, two of them are thicker and thru the body stiffening bars underneath, looking at them they did not appear OE. Having a cuppa so I looked on line at images of the engine cover and some appear to be like mine with 12 holes and but most have 10, but the ones with 10 don't appear to have indentations to clear the bolt heads of the stiff/bar underneath. I was thinking of opening up the two extra holes to clear the bolt heads but then the cover would not be sealed in the event of a engine fire?
If you have the 10 bolts how does it clear the bolt heads or aren't they there? mine is an early car so I presume it was a modification, the F covers I looked at had 10 bolts but I don't think they had the stiffening bars.

Yeah, the 10 bolt is the original, used for cars before they fitted the strengthening bars in the TF. So those two bolts are absent.