I see this thread has come back to life. Let me pick up on an earlier point made by Porrohman, before I reply shortly on the asphalt overlay question.
I seem to recall reading that EDI was one of the V-Bomber dispersal airfields during the cold war so runway 12/30 must presumably have been much stronger than 31F/C/X/T back then.
I got curious about that, so I derived the ACN of a Vulcan MkII bomber (such information is not normally available). At its normal maximum operating weight of 81.6 tonnes, the ACN is about 20 on a “C" subgrade; at its war overload takeoff weight of 90.8 tonnes, the ACN is about 24 on a “C” subgrade. I say ‘about’ because the exact undercarriage and tyre spacing is not available to me. However it does show how effective the 8 tyres per main gear leg were in reducing the ACN; modern civil aircraft at that sort of weight (A321) with only two tyres per main gear leg have ACNs around 58/C.
So the Vulcan bomber would be OK to operate on the 12/30 runway with its 31/C rating.