273?

Mine is a 270 model that has a 273 2 bbl. I debating if I'm going to rebuild my 273 to make it a 4 bbl. or put in a 340. I have a 8 3/4 I want to swap to. Mine other question is will the whole brake setup from my 7 1/4 bolt onto the 8 3/4 housing? The 8 3/4 housing I have has axles with SMP and backing plates.