DJ,

Thanks for the clear and informative post.

"The shop manual says the exhaust pipe and muffler are welded together but can be cut apart to replace the muffler (and that if you ever replace the exhaust pipe, you'll also be buying a muffler....because they're welded together)."

http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0803.htm

I had never read that section of a Shop Manual and I am somewhat amazed to see that the exhaust piper and muffler were one integral part on the original truck.

You also posted: " . . [and] then probably buying a straight tail pipe from the muffler shop . . "

Most likely, a "straight" (no bends) tail pipe will not get "around" the rear end. (The tail pipe extends from the muffler to just below the rear bumper (if you have a rear bumper).

As a "postscript": has any reader/member come across a truck that still had/has the original exhaust-pipe/muffler welded-together combination?

I have bought exhaust system parts (54 pickup) from Jim Carter, and they have fit fine. No one seems to sell the correct tail pipe for a panel body truck.

ooops, I did a search on that tail pipe and bowtietim corrected me in 2005 - Chevs of the 40s sold/sells that tailpipe
https://www.chevsofthe40s.com/shop/search.lasso?partno=3689574&Go=Go