I looked at the Atlas frame on line in the parts list. Based on the drawing, it does not look like the P&D conversion will be a drop in. I think you will have to drill and tap the aluminum frame to install truck bolsters. You have to cut and drill the original IM frame for this also. And it looks to me like the pilots and steps install totally differently on the Atlas. On the IM unit the pilot/step assembly is part of the shell and wold have to be cut off. On the Atlas it looks they are separate parts that screw on.
As an aside, Des Plaines hobbies in Chicago (they have a web site) sell machined frames for these units that fit the P&D drive and provide weight. They are pricey, but nice. I think 60-80 dollars apiece.
