I´ve seen the photos of Goodwood. Too bad I couldn´t participate. Your roadster looks good without the roof!
Don´t sell the cars. You´ll never get them back once you are married.
Maybe you could offer another deal and promise not to buy a motorcycle in the future (not that you intended that, of course!).
You could also promise never to frequent that Gay bar you used to hang out at and of course never go skinny sky diving again either.
All these things you are prepared to forego for her, just make sure you keep the cars, and a third garage for any future acquisitions
Alternatively hide them at my place and just develop a very important supplier in Surrey who needs constant visiting ...