Captains bars are not a guarantee of a 261, 1953 Power Glide 235's also had them.
1954 261(first year for 261) will have the high mount water pump and Captains bars.
If it has the low mount water pump(1955 2nd-63)and Captains bars then yes, 261.
Unless it is a crate motor, and not stamped, the stamped number next to the distributor is best way.
