First off - welcome to this happy band.
Secondly I know less about XBRs than I do about solving middle east relations. However. Was the bike running and is there any information as to why it stopped running? Just wondering if it were something like a bent valve, then could we not be increasing any damage by kicking it over loads? Would it be an option to run a little engine oli down the plughole to produce a very temporary seal. If there is compression for a kick or two with oil - it is gas passing the piston, if there is not then it is gas getting out from else where? Maybe I am being a bit of a worryguts, but I used to have a Superdream that "lacked" compression and would not start unless you jumped up and down loads on the kick / ran the battery down on the lekky start. Thought it was knackered bores / rings. turned out to be a couple of valves that were approaching time expired and were splitting. Eventually one broke and dropped into the engine, the con rod did nto like this intrusion and came out to make its feelings known...
However having never even ridden an XBR let alone pulled one apart I would nto listen to me but would listen to others...
R