Just wondering if you have to use the two
pieces together, or can you use any of
the plates you have attached to the
bottom of the cameras, such as the
ones that come with the 503 heads?

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=241139&is=REG

In other words, will the bottom piece of the
577 work with other Bogen top pieces?

Dave,
I have and have used the 577 with the cam plate from both the 501 and 503. They are all basically the same and interchangable.

HTH,
Don B

Not all Bogen plates are interchangeable. Check the specifics for the one you want to match to. But 503 works with 577.

Thanks, Don and John. That's what I have, the
503, so now I know.