I installed a Pypes 2 1/2" X pipe system on my '68. System was a real bearcat to install. I had to "adjust" both over the axle pipes to get them to fit. Their Street Pro mufflers were too loud in the car. Changed them for Flowmaster 50's.
I went to local Meineke w my 69...a friends brother runs that shop...paid $500 (10 yrs ago) for a custom 2.5 inch system with H crossover...2 Flowmasters 40 ....then added chrome ends with dbl bend downs , botght from EBay, but looks like the original pipes behind rear wheels. didn't seem too hard for them to do...
Had local muffler shop do mine also. Do you have pics of your Exhaust tips? Looking for my 68 with 2.5", just have the pipes sticking out for now, wasn't sure what i wanted back there.