Baseboard oil fired hydronic two zone heat. I have a noisy circulator that I guess needs to be replaced. My problem is I can not deciper what kind of circulators I have. They are twenty plus years old and are 5" from flange to flange. There is two allen cap screws diagnally holding the motor on to the pump housing. The only circulators I can locate are 61/2" face to face. Any suggestions? Thanks in advance.