1971 GMC C3500 Exhaust

[-Malcolm]

Hi new here to the page.
I have a 1971 GMC c3500 regular cab dually with a 350.

-Was wondering if anyone has removed the factory Y pipe at the manifolds and installed Dual intermediate pipes to the factory manifolds?

-Do Exhaust parts for a c1500 fit the c3500?

-Have seen flow master makes a set of intermediate pipes 2.5" prt#81072
but does not say if they will fit a 1971 c3500.

Thanks in advance for input and comments below.