While I did not do this on a Ranger, it was a Lund. Since I may use my boat for walleye fishing the same day I salmon fish, I wasn't interested in installing a rear beam. I took the rear decking off and engineered an anchor point with 3/4 inch plywood and metal plates. I had the metal plates cut wider than the mounting base for my downriggers. You'll have to take a look at what is under your rear decking and see if it is possible. Obviously the screws that hold your decking down aren't enough.
I just have the Cannon mounting plates (see photos) that sit on rear deck if I'm not salmon fishing. They sit down in the carpet pretty good. Then I mount the pedestal to those. It only takes 10 minutes to install the downriggers. If you do pedestals, just make sure your overall height is enough to clear your gunwale if you want your downrigger to swing out the side of the boat. I put the pivot base on top of the pedestal so I can rotate the riggers out to the side when fishing and then to the back for transport.