FYI, the only difference between a Giga X Pipe type BB and a Shimano Hollowtech 2 is that the GXP has a shim on the non-drive side, and the dust cap has a slightly smaller opening. If you press out the shim and trim the dust cap, a Shimano crank fits perfectly.

Conversely, if you put one of those shims into a Shimano BB, a GXP-style crank fits perfectly.