How do you convert a 1988 Caprice Classic from single exhaust to a 'true' dual exhaust?
The only main problem you are going to have is there is no dual exhaust cross member available as far as I know, but a good custom pipe bender at a muffler shop can pancake the driverside pipe. Which means they square off the pipe where it won't hang below the crossmember's nonexistant hump. If you run dual after market converters it should pass emmissions.
If you want the look of duals, go to Big Al's muffler and break. They do cat-back (from the converter back) duals for $200. I don't think putting true duals on this car is worth the money as you need another converter not to mention the problems mentioned above.
Actually, you can get a dual humped cross-member out of an older model Caprice cop car, but they're hard to find.
No, that is not true. No 77-90 B-Body GMs had double hump crossmembers. Even the 9C1s had a single converter that split into two pipes.
One option is to take the cross member to a good welder and have him cut a section out, flip it over and re-weld it. Then use 1/4" angle iron to reinforce the cross member. Use it on both sides of the C M and extend the angle iron 6" in either direction from the out side edge of your modification.