[MarkBardenwerper]

I think the chassis are essentially the same except for the addition of another tube. Pretty sure they are the same dimensions. In effect it is a minor upgrade.
Here is the electronic side
http://www.tuberadioland.com/philco41-255T_main.html
(I'll wager the 485 is a 455 on stilts. Same speaker trans part no.).
Some sites say the sound is much better, others say, not much.
Additionally, the faceplate has a minor difference. Mine has a an additional box below the band indicators that says, "push but." Instead of the cable operated single indicator light, the 485 has a switched row of lights (missing here).
But the output section looks to be the same. It might be an interesting swap, but I think I would just use it for parts. Here are top and bottom views of the 485.