Aye Richard,
This will need checking; but, I think that the Honda Part Number 12251-MK4-602 cylinder head gasket fits the XBR as well as the XR500!
This needs to be confirmed!Might I suggest that you contact one or both of the following, giving full details of the model, engine number, bore etc.
Firstly, contact 'Eastwood Racing' at Swanley in Kent, they are the Wiseco Importers and stockholders for the UK and I have used them for replacement SRX cylinder liners, pistons and matching gaskets, all good quality and good advice if requested.
Eastwood's Home page:
Eastwood_Honda_RacingEastwood's link to Wiseco Honda cylinder, piston and gasket sets:
Wiseco Honda cylinder, piston and gasket sets.pdfAlternatively, I suggest that you contact Mark Apland in USA. He has a goodly list of items for the Honda GB500, but not having dealt with XBR's and GB500's I cannot say about their interchangeable specific dimensions. Link:
Mark_Apland's_'Thumper_Stuff'Hopefully between them these two suppliers should get you and others out of a hole, with parts of known quality and reputation.
Lastly, and an unknown quantity to me are these Dutch suppliers; worth a call if others cannot oblige:
CMS_NederlandMy regards, Bill