Adding headers and new exhaust

[mike's1965]

1965 C10 truck with 396 big block, adding Edelbrock pro flo 4 multi port fuel injection, bought new summit coated headers for BBC C10 trucks, and bought a 3" header collector that has O2 sensor bung installed already, may order 2.5" collector with bung as the 3" looks huge, not sure how hard 3" pipe is to find, and run in truck.

Seems no shops in Phoenix or Arizona offer mandrel bending, but found a shop in Bakersfield CA that does it.

I want to have the exhaust sorted out and O2 sensor bung ready before adding the fuel injection, test for leaks and a few drive cycles to retorque headers so there are no leaks, any leaks can throw off the sensor while it's self learning.

See dual exhaust kits you put together yourself, however I think most are made for small block Chevy.

Bakersfield is a long drive with no overdrive, 396, TH400 and 3.73 gears, and I would probably put the headers on here at home, just to make sure they fit, also so they can build the new exhaust from headers back.

Could also try to scrounge my existing exhaust which I took from the donor 1974 Chevy C10, way back then I didn't have the $ for a new exhaust, and the 1974 exhaust could not be run straight like it did on the '74, I had to cut it short and point each muffler and pipe in front of the wheels on the '65, because of the trailing arms, it works but is amateur looking, lol.

These shops in Phoenix act like mandrel bent is overrated, unnecessary and I don't need it.

Looking under my factory stock 1999 Corvette, I see mandrel bends, if it's not necessary why did GM spend the $ to do that?

Would you drive that far for a good quality exhaust?