I made a 2-1/2" for my 69 C60. I ordered a kit and cut off all of the slip joints and tig welded mine. I went all the way to the rear of the truck and pointed them straight down with a set of knock off 40 series Flowmasters. I also out in an H pipe.
I also made the exhaust on my 52 willys truck with a 460. 3" duals all the way back with an H-pipe. I'm running the same mufflers you posted a picture of on that. They have a nice smooth rumble with almost no drone. High rpms they are very loud.
A word of advice is to NOT put your mufflers under the cab. Put them under the bed. I've made multiple exhausts and always put the mufflers as far away from the underside of the cab as possible. If there is any drone from the exhaust it will resonate under the bed and not into the cab.
