No kidding? The rim inside the bottom to hold the standard 235 thermostat is a different diameter? N/M it IS a different diameter. Unless you need that extra port, it would be easier in the long run to get a 235 housing SET. Are the 261 thermostats even available any more? If so, is there some reason a person would want to go with the bigger thermostat? Since the inlet on the block is the same diameter as the 235, I cant imagine it being better water flow.
