Brendan, glad you enjoyed it. Re 27a, Chambers gives OF = IN (albeit as the 18th definition), OED is a little more explanatory:
"One of, a member of. Hence: belonging to, included in, taking part in. Now chiefly in to be in (the world, etc.) but not of it. Cf. man of the world"
So, pretty obscure, but needed to make the surface plausible.