That should work, thanks! Also we can have SQL-visible functions to get amsupport and amstrategies and use them in the regression tests.
SQL-visible functions would be preferable to storing it in pg_am as keeping the params in pg_am would limit the extensibility of pg_am itself.
I actually meant just two particular functions (not per AM) which both get AM oid as argument. They should call amhandler and return amsupport and amstrategies correspondingly.
These functions can be used in regression tests to check opclass and opfamilies correctness.