The dash temp sensor is in the left head we learned the hard way on our 1992 454TBI. The one in the right head turns on the radiator electric fan at 210F.
I expect you bought a stock water pump. The shop that replaced ours caught NAPA's mistake because he had the old one in hand. It delayed the job a few days and the shop owner state there was a noticeable difference between the stock 454 and MH 454 water pumps. Cross out the part number and insure you have the MH 454 water pump and not the stock one that GM put in their trucks or cars.
If you asked for a 454 water pump I expect you did not install the version for the 454 when used in a MH application.