Put my 75 Eldorado on the lift today and it will be necessary to replace upper and lower ball joints and left rear body mounts. I would also like to install a straight pipe in place of the Catalytic Converter. Who help me source these items?
Are you sure the uppers are shot? These cars eat lowers and wheel bearings but I haven't seen a bad upper yet. The GMC RV people probably have the best stuff these days and even offer rebuilt arm assemblies just be sure to tell them its for an Eldorado when you order.
Body mounts I'm not sure I have heard of anyone messing with those recently.
As for the exhaust its pretty much a custom job these days so if you can't do it yourself you will just have to see what local shops have to offer. Are you having issues?