We do have a fair number of R65ers in Britain - there might possibly be one or two not too far away from you who might offer hands-on assistance.
The knocking of crank/conrod bearings is -to me- a more hollow, low pitched sound that often only shows up at RPMs a little above idle, even without engine load, whereas spark knock/pinging is rather RPM independent and only under engine loading conditions and could simply be bad gas, plugs, and/or misadjusted carbs.
What is the mileage on the bike - and does it seem to be accurate/reflective of the condition of the bike? Has it been sitting, unused, for many years? Do the frame serial number (on right side headstock) and engine number (above oil dipstick) match? If you go to check it out, bring a digital camera with you and take plenty of pictures. Don't be afraid to lie down and take pictures of the underside of the engine/oil pan, cylinders as well as the prettier topside bits. You can post pics here and we can help with trying to determine the condition/repair items based on visible leaks, rust, etc.
The European octane measurement formula and the United States octane formula are different, resulting in lower numbers for the US octane measurements for what would be an equivalent fuel formulation in europe. However, I don't know if the european communities have 10% ethanol in their gasoline, which we have pretty much in every state in the US. This adds other fuel issues/challenges as it is for us, and now the EPA is planning to raise the ethanol percentage to 15%.
