Swapping a 455 in place of my 307 on my Cadillac Brougham, 1987.
(With trans and other)

I found on ebay there are factory 455 exhaust manifolds with the 3 bolt exhaust flange for single exhaust and can take a crossover pipe.

Do you know if I can buy those 455 manifolds and use the crossover from my olds 307's manifolds?

 

The SBO crossover will be too short for the 455 application.
There is a current discussion about the differences here:
https://classicoldsmobile.com/forums...over-pipe.html

 

Ok thanks. Would have been easier because I could have kept the single exhaust without much effort, but since I'd have to get a pipe made up, I might as well get a dual exhaust for not much more.

I have been looking at these for a dual exhaust, looks pretty good:
http://www.ebay.com/itm/Oldsmobile-C...hEn88w&vxp=mtr

Says 455 big block. I mostly just wanted to verify that it will for sure fit the 455 since I'm here.

 

Those manifolds will fit your 455. I don't know if there would be enough clearance for your conversion though.

 

Those W/Z manifolds should work fine in your D-body Caddy.