Just a thought, Darin:

If you know any military types that come to the States to train? I know when I was in the Air Force we would routinely tote parts abroad to our friends in the UK. Might have been a bit on the side, but I never had a British Customs Inspector ask me if i had, "car parts." (They asked all the standard, "tobacco", "guns or ammo", etc - but never asked, "have you a carburetor in your bag?"

I know heads are a bit heavier, but a pair split between two bags is certainly doable..

Good Luck,
Glenn