As for fixing the dents yourself it is possible with a press to do it with a few blocks of steel, one would need to be a perfect and square fit inside the reciever between the 2 rails, would have to be snug to be sure you did not push it out of spec when you flatten the roller bumps, then use steel block on the top and the press. You would need to make a T of steel for the underside of the reciever and other rail. If you have a good shop and metalworking skills you could do this. BUT if you are not careful you could make an expensive mistake. The press has power to stretch and squeeze the flat out of spec so do not John Henry it. Just a gentle squeeze that will push the dent back, would even put blue painters tape over the area to minimize possible finish marring from the steel pusher blocks. Honestly the best safest way would be to use the the mandrel that RTG Parts carries that slides into the reciever has exterior peices that fit into the rail slots and trues up the shape of the reciever bringing it into specifications. But this is an expensive builders tool and you are very likely to mar the finish on the reciever in the process.
Each method has its drawbacks but it can be done