Welcome to the forum, David. Now, that's a downright cool period survivor. Definitely worth dusting off.
Unless there was some mix/match of engine components going on there, it looks like the engine is likely a later-half '71 XS1B. Earlier engines had plastic buttons in the head fins, 4-bolt camchain tensioners, gusset reinforcements behind the left-rear cylinder stud. Yours has the later type "B" XS2 tensioner, no reinforcing gussets. Engine serial number could confirm.
Go thru these threads and imbedded links for discerning info on the front motor mount.
http://www.xs650.com/threads/engine-interchange.50643/
http://www.xs650.com/threads/xs1-engine-mounts.47629/
Unless there was some mix/match of engine components going on there, it looks like the engine is likely a later-half '71 XS1B. Earlier engines had plastic buttons in the head fins, 4-bolt camchain tensioners, gusset reinforcements behind the left-rear cylinder stud. Yours has the later type "B" XS2 tensioner, no reinforcing gussets. Engine serial number could confirm.
Go thru these threads and imbedded links for discerning info on the front motor mount.
http://www.xs650.com/threads/engine-interchange.50643/
http://www.xs650.com/threads/xs1-engine-mounts.47629/