SOTP Vintage Series
Main Motorcycle: The one between my legs
Join Date: Feb 2009
Location: Upstate NY
Other Motorcycle: A few
Extra Motorcycle: Yes
A fallback is to use the torque specs for standard fasteners. Use Grade 5 fastener settings and you should be safe. Needless to say, you'll have to measure your Brit fasteners to find an equivalent SAE or metric fastener, but it works if you have nothing.
Also, be aware of what using things like oil, anti-sieze and thread lockers do to torque settings. As others have said here, torquing a bolt is just a way to measure bolt elongation, which is what you are really doing. So, if you have done something that results in more elongation for the same torque reading, you are over-stretching the bolt.
Lots of info on this topin on the internet. You can find bolt torque charts there as well.