I have read all the timing posts and have a good understanding of it, but I have a question. 

What is a common RPM for the mechanical advance to come in and at what RPM should it be at max advance?

I have talked to Lee Johnson in AZ about rebuilding my distributor and will be sending it to him. He said he can set it to how I want it. 

The info about the car:  56 Mercury Montclair, stock 312, stock rear end gears, the distributor is a 57-59 Ford, Ford 4100 carb.  The car is not a hot rod, I drive it very "putt-putt", but I do like to cruise at rural highway speed (55-65 mph).  

I don't know what this particular distributor came out of, but the mechanical advance is not working. I totally disassembled it, cleaned it, reassembled and installed. Everything seems normal and moves freely, but it still doesn't work. It has two different springs, one light and one heavy. Even with my fingers, it seems like an unusually heavy spring tension, but I don't know how stiff is normal. I ran it up to 4200 RPM and no advance.  
I will be sending it for rebuild, but I need to have an idea of how I want it.

So that is the big question.... what has anyone found to work well on a car like this for when the mechanical advance comes in and when should it max out and what would be a good max advance amount?

I appreciate and thank you for help.