Denny,
Have you checked the operation of the thermostat (a Dole pellet by-pass thermostat was originally used, I think)?
GMC kid 7530,
My 1960 261's water pump (from a school bus) did not look like Denny's. It had an extra port (or two); and, the thermostat housing had a port on the bottom, like Denny's.
Years ago, someone posted the purpose for those ports (sqeeze or 3B or Mike B?) - a by-pass hose. I wildly guessed they were for a heater at the rear of the bus (or, maybe for a transmission warmer/cooler).
Maybe someone will post an answer?
You may plug the holes if they are not used (mine were plugged with hex-head steel plugs).
Years ago, I used a smaller truck's water pump and thermostat housing, to better match my 1954 radiator. Today, I use a water pump relocation plate and a 54 water pump and thermostat housing.
