I'm thinking of changing my old Stradale style fuel filler caps to Monza style, I notice on eBay there's a 2" and a 2.5" version, has anyone fitted these to their car and can recommend a size which fits best?

I'm assuming I'll have to machine my own adaptor or chop the tank a bit and come up with another fitting arrangement - any other easy/neat solutions out there?

Vince.