i did all the body work on my 46. i was in the same boat you are in
i had to learn enough to get the job done. i did some of both butt and flange joints. im sure that a pro knows how to flange correctly
but on that thick metal on these old trucks the flange made a hump
that was hard to hide. the method that worked good for me in a few
spots was to make the patch bigger than the hole and put it behind
the body and spot weld them in. i finally just dove in and got started and let each panel sort of tell me how it wanted to be to look nice and be strong. oh and the tool that made all the difference was a cutting wheel on a 4" grinder.