First off, welcome to the forum.
The trailing are issue was only on the Roadmaster RR4R chassis so you wouldn't have that issue on your Diplomat which is an 8-bag chassis.
As for the bushings, if you have the equipment to raise the coach and remove the trailing arms, the job is pretty straightforward. Having access to a hydraulic press will also be necessary as they are a press fit and require some pressure to remove and reinstall, especially after some corrosion adds to the equation.
Personally I would not replace them with the OEM bushings. I have only been using the polyurethane bushings made by ATRO and they are hands down a much better bushing AND they firm up the H-frame suspension as there is quite a lot of movement allowed by the OEM rubber encapsulated bushing.
Mike
