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Based on the pictures I see of the 1542 on B&H's website, it looks like the tripod legs should be able to fold up either direction and not contact the ballhead (based on these pictures)
If I were looking for a ballhead to hang a 5D and 70-200 on, I would go with the BH40. But at the same time, if you're using the tripod collar on those longer lenses, I would imagine that you can balance the setup ok and be just fine. I believe you would certainly want a larger ballhead than the BH30 of you were going to be using it often or with lots of moving around (recomposing, etc). Like I said before, the BH30 works fine for my 5D and 24-70, but I also only use a tripod once every few weeks, and I don't typically re-compose very much, so my setup is typically aligned, then locked down until I leave. The more you use the ballhead, the more you'll want those extra features like ball tention knobs and built in levels.