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....