I was told years ago by a walker rep that it is very important for new cats to get up to temp as quickly as possible after installation to ensure that the substrate (honey comb) expands and sticks in place properly. On a modern car they heat up fast enough it's just get in and drive normally, but on a carbureted engine he recommended that as soon as you feel comfortable after starting the engine to rev it to 2K and hold it there for 5 minutes, then let it idle and check inlet and outlet temps of the cat looking for at minimum 50F higher at the outlet than the inlet, but closer to 100F is more ideal. Can go up to 15 minutes checking every 5 minutes. If they aren't lit in 15 minutes the cats are to far from the manifold, or the system needs an air pump.
I have a working air pump, so my only concern is that I have 2 cats now instead of 1 so that's 1/2 as much volume of exhaust, will that affect temp??? So I fired the truck up let the engine run for a few to get the oil circulated and ran it up to 2K. I immediately thought to myself it's going to get stinky in here I forgot to open the shop door. Much to my delight after 5 minutes of running I got out of the truck and noticed the lack of odor in the air and a little condensation dripping out of the tailpipe. A quick check with an IR heat gun confirmed what I suspected, both cats were already up to temp and working quite well.
As for the drive after work, I had to run the truck for 2 hours a little traffic leaving the city, then a short bit on the freeway with most of the drive on country roads. I'm happy to report that I was not assaulted with with any stinky exhaust or oil smell (In the midst of this I had a valve cover gasket start leaking). It was just a nice and plain, pleasant drive home, no exhaust sucked in the heater and none even with the window open sitting in traffic. So far it seems like these cats are actually working better than my old single cat did, but how knows how old that one was.
Also the addition of the cats mellowed the tone of the turbo muffler, which is not unexpected but it puts them right around the volume and tone I'd wanted in the first place so I'm VERY happy to get new cats back on.
I'd say that if someone is looking to add cats to their truck even a dual exhaust truck where two are required it'll work just fine with a modern universal honey comb type cat, mounted behind the transmission cross member, but I should also mention that my truck has a functioning air pump, pumping air into the exhaust manifold, which helps the catalytic converter (s) get up to temp faster and start working quicker and stay at temperature.
I have to put about 200 miles on the truck tomorrow to haul feed back to the farm, so we'll see how it goes and I'll report back, but I'm thinking this will be the end of the BS and me fiddling around with the exhaust.
@DoubleDingo tagging you since you have expressed some interest in putting cats on our truck, pic of the install in the above two posts.