No, you're still confused
You don't need a dishpro adapter since the 4900 is already working. Just the SW44.
Looking at the switch test info on any of the existing receivers will tell you what type of equipment it is. Based again on the fact that you have a 4900 which is pretty old, I'm guessing it's probably two SW21's, sometimes the installers mount them on the back side of the dish antenna. But the switch test will tell you for sure. If that's the case, you will have to climb on the roof and find them, replace with the SW44, and run the additional one or two cables from its 3rd and 4th outputs.
Also, the SW44 has a "power inserter" module which is placed between the SW44's output 1 and the first receiver, (preferably inside the house).
The diagram on page 128 of the 721 user guide (I'm more familiar with the 721, I have one, but the same install diagrams work for all models) can explain it much better:
http://www.dishnetwork.com/downloads/pdf/technology/721/721_User_Guide_part3.pdf
Or, you can accomplish the same thing by swapping the existing LNBF's with a Legacy Quad (page 127)
I recommend going over the entire chapter before trying to do it yourself.