Jon -
You are better off locating the clams 'foot' (byssal gland thread) and using a sharp razor blade to cut it as far away from the clam body as possible. If you just pull on the clam it may tear and possibly injure the clam.
As for the acans, if they have attached to the rock I don't know how you could remove them. You might try a hammer and chisel a few inches away from the coral to try and break the rock up to a smaller size so that it would fit better in the new tank...