More 65 Valiant 273 to 360 swap questions

I agree with Pishta
If the 360 is keeping the 2bbl cam, then headers on a streeter are optional, for all the reasons he lists.

BTW
I once put a 340 in a 65V100 wagon. I dressed it up with the entire 318 top-end and cam. From the decks up it was 318. Then I installed some fenderwell headers,go figure. Oh yeah, I was about 23.I called it my big-bore-teener.
Man, that car was a blast to drive, even with the 7.25 rear. The 904 gave up in the second summer. The rear was still taking a licking!
The 360 is 20 cubes bigger, and was born with a bigger cam, and bigger heads. It will be bigger fun!