sorry, my answer was maybe a bit too short.
There are two standards for full block Cockers: pre-2k and post 2K. CCM may not have the pre-2K in stock, but you can be sure you can buy a 2K specs pump kit from them at any time.
Plus if you want to do some custom milling you need some meat on the body. 2k and 2K1 bodies are perfect.
The Prostock is a particular model released a few years later which is very common so it might be a good candidate for milling.