Some reading. TXXS knows his early bikes...........Post #3 in this thread might help
https://www.xs650.com/threads/1971-xs-1b-xs1f.35336/#post-357851
https://www.xs650.com/threads/reinforcing-gussets-on-early-xs1-xs1b-engine-cases.55960/#post-616844
https://www.xs650.com/threads/after...t-was-an-xs1-is-an-xs1b-help-id-please.60480/
https://www.xs650.com/threads/is-this-an-xs1-f.60088/#post-702908
https://www.xs650.com/threads/1971-xs-1b-xs1f.35336/#post-357851
https://www.xs650.com/threads/reinforcing-gussets-on-early-xs1-xs1b-engine-cases.55960/#post-616844
https://www.xs650.com/threads/after...t-was-an-xs1-is-an-xs1b-help-id-please.60480/
https://www.xs650.com/threads/is-this-an-xs1-f.60088/#post-702908