I replaced my filler neck on my old cab and I got mine from ECP. IIRC, the tintop is smaller than the cab and is a heck of a lot cheaper. You can use the tintop one with some extra pipe and a clip to make it fit apparently. Mine from ECP was about £96+VAT but the tintop one was about £30+VAT. A foot longer seems quite a lot though. Are you sure they've actually given you the correct part ?