as this car wasnt a 400 to start with (judging from the hood), you most likely dint have 3 items that were on 400 `s and AC cars...and when you put a 455 in it those would be required 1) X filler panels 2) lower baffle 3) rubber or 'masticated' fillers on ea side of bottom of radiator
If you have those...keep looking, but if you dont have those , I bet installing those will bring you down 20-30 F....
I have already run my car with a practically brand new 455 in Oklahoma summer heat WITHOUT my original x panels, lower baffles or rubber fillers (to be installed after I get it painted) without any cooling problems whatsoever.
It's my opinion that if you have solved your cooling problem, the added benefit from those factory fixes is not all that great and should not make the difference between boiling over and not.
maybe.....when I got my car it had been a 350 car and no AC...PO had installed a 400...evidently it ran hot as he added a pusher help fan ,which didnt help...I drove the car back from DFW area to Houston...235F most of the way ,240 uphills...I got rid of the helper fan, added one missing rubber filler and the X fillers, reduced 15F right there...for some reason my car had a rubber filler and the lower baffle (must have been installed along the different ownerships at some point)....after several other small Items over the past 11 yrs I got the car to run 200-205...last year I added a 3 core Champion alum radiator...now runs 190-195 F
