You may have to switch to a 4 shock setup to have clearance for the header. Many many years ago, I had a BB maxx as did a friend of mine. He used dynamites conversion kit and I used XTM's. This was way before the 3.3 existed.
With a big block, the tmaxx diffs would grenade. The 2.5 maxx diffs weren't that great. I got tired of replacing diffs every other bash and gave up on it, then went with a true 1/8th scale instead. If yours has revo spec diffs, then it should be fine with a BB as I haven't had many issues with my LRP28 big block revo. When I ran it a lot, I'd have to change out the slider axles every other season, but they held up pretty good.
One other thing, the transmission in the old maxx was weak and the BB would rip through the gears within minutes. I replaced all the gears with RRP steel and only had an issue once or twice with the two speed shaft splitting in two over the few years after that I ran it.