It depends on your budget whether they're worth it.
I am finishing up a 350 - 454 conversion on my '87 now. The 454 came from a '76 3/4 ton lwb.
I still have the original bracketry from the 454, but when you install headers, that changes everything on the driver side of the engine with regards to A/C and PS mounting.
To fix this, I used the ULTRA Serpentine system from March with he Alternator / AC bracket in one. You can see it below.
I don't have the A/C compressor they recommend yet but will soon. All three pieces (PS, ALT, A/C) are available from March too, either chromed or billet.
Kenny