SRAM gxp crankset on italian BB shell
 

I'm interested on a frame with italian BB shell and I already have SRAM groupset lying around
as my understanding that an italian BB shell is 70mm width and a SRAM gxp crankset is intended for 68mm shell
would this be a problem?
currently I don't have access to SRAM GXP italian BB, can I instead use shimano HT2 italian BB and use some kind of shim/adapter? anyone ever tried this?

No, just get an Italian BB.
SRAM Alloy GXP Bottom Bracket | Chain Reaction Cycles

What he said. SRAM is bigger on one side than the other. SRAM = SRAM other than the older stuff they shared with TruVativ and Bontrager....