Mmm would really need to know the measurements i.e how much exactly has been taken off the head....pity you hadn't measured the c/r when building it if it's had that much taken off the head. The reason i say this is because you can run pretty big bhp on standard c/r and higher c/r's too, mine was running 245bhp with no detting issues on standard c/r pistons with a head that had been skimmed a couple of times (1.5 bar boost) so if the engine's fine i'm sure someone who knows what they're doing could set it up ok. If you need to lower the c/r slightly you could always take a bit out of the head (the bowls) instead of skimming pistons, would need to be done accuratly though etc but i wouldn't be too sure that's your problem, especialy if it's still detting running such low boost......