Heres what I did on my Mark 4 non-steering pump engine for added protection. I added a third belt to handle the circ pump in case the alternator belt breaks or blows off. Its a Napa 7320 and fits fine. To put it on, just remove the water pump pulley. On the steering pump engine, that belt is the backup driver for the circ pump.

Thanks for the tip, I have blown a belt before and was lucky enough to have caught the temp rising on the gage and came back on one engine.....I will be doing this to mine....Thanks, Fred

And to make matters worse, the alarm senser is mounted in the thermostat housing which is still getting cold water from the raw water pump. So, you blow the alt. belt, the circ pump stops, the engine starts getting hot, but the alarm doesnt go off. The only indication is the alt and water temp gauge. Its amazing how hot that engne can get at WOT before you see those gauges. I moved the alarm sensor down to the intake manifold where the gauge sensor is.

Its a good secondary protection but another pain in the ass when you only blow the raw-water pump belt! ....been there done that!

F31,
Thanks , I am going to crank driven raw water pumps this year and I was thinking on doing the same thing . You saved me the time and agrivation finding the correct belt.
I have a 272 SR-1 and getting to those belt driven pumps with twins is a PIA
Thanks again

ttt