Charley - A web check shows neither of the Felpro B-2 or B-3 gasket sets fit a 261. The B-2 is for 1937-53 216's and 235's, while the B-3 is for 1953-62 235's according to the Felpro site.
Felpro only lists one full engine overhaul gasket set for all 1954-62 Chevy 261's -
FS 7782 B.
Lots of sources offering the Felpro FS 7782 B sets, like this one from
Rock Auto FS7782B, which happens to be the best price I found across all offers.

Hope this is helpful.
