Hey Andy,
Yup brought back headers in a spare case. Read up on what you can bring back auto wise, and only fluids were a concern, of which I wasn't transporting any. I paid for an extra case and just took it with me and prayed. Granted I never had the receipts or any documentation with me for the headers. I sent those via post, to myself at home. That way there was no way of Boarder control adding VAT to an unknown price of product. They were essentially 'used' and a 'friends'. I've been 10 times to the States, never been caught in customs and always had goodies with me.
Engine mounts are not too bad but you will notice them. I'm on very stiff suspension so you know the modification has been made, but it's not my daily nor an issue to me. Nothing that's too off putting at all and I'd say even less noticeable on standard spring set ups.
I don't have a Sikky prop, although I am hoping that a carbon prop may find its way to me soonish 🤞🏼