Does anyone know the size or part number for Walker exhaust system true dual exhaust ( 2 mufflers/ 2 tail pipes? I have the 2 front Walker header pipes but not sure what size/ off set mufflers I need.

I don't have a catalogue handy, but you're gonna have to tell what engine you have for someone to look up a complete system for you to be sure the front pipes are correct. Also, do you want the system that has the resonators under the rear seats or do you want to eliminate them, and also, is it a coupe or convertable.

69 hard top coupe, 327 powerglide. These header pipes were from a walker dual exhaust system I had on the car with the muffler under the rear seat 2 header pipes into1 muffler into 2 tail pipes. I was told by a knowledgeable person the header pipes will work with 2 header pipes into 2 mufflers into 2 tail pipes.

can anyone help me with this question?

Steve , out of my old memory, I can say the the orginal GM double wrapped header pipes were 2 1/8 or 2 1/4" leading into your resonator mufflers before going over the axle into the transverse muffler. This was the stock setup.
The other set up was the deep tone exhaust that did not use these front under seat mufflers or resonators .
I ran this type deep tone on my Z for a long time before going to 2.5 Flowmaster kit 17104. Hope this helps.