When you go from a SB 350 to a BB 454 on a 72 with taller vavle covers for rollers will the SB AC compressor brackets mount on the Big Block also? Or does it need changing also?

The compressor is just fine.......... You will need a complet set of 69-70 A/C brackets/ Or a complet set of 71-72 A/C brackets for a BIG BLOCK.
With the tall valve covers, You will have to work on the bracket that goes over the valve cover. Shim it ,Spacers, You will figure it out.
Bob