Starting a BB Duster project

Same issue with my Duster...stock 383, Champion 22” radiator, new high flow 180 thermostat I checked on the kitchen stove top, 7 blade fan w/no clutch, repop modified shroud. Runs 160 or so usually. The only time it will get 200+ is idling for an extended period during our blast furnace summer...I have checked my gauge with an I/R gun.....