If you don't mind making the change at the flange end, you might consider trying BBC Patriot fenderwell headers for a Tri 5 Chevy. The spacing on a BBC is probably closer to a 302 than other type of engines, and cutting the flange off and reworking to fit a 302 Ford flange might be easier. The other bonus is the Patriot Tri 5 BBC headers are just over $200 new, so a very inexpensive set to start with. 2" primary tubes, and 3.5" collectors; so very good flow for almost any engine build you'd want to use. Might have to slip 1.75" tubes inside to reduce down to fit a 302 flange.
Have you thought about a pair of modified fender wells for a SBC. That's what I did for my 53 with the 428. I got some Patriot fender wells from Speedway and got a pair of Ford FE large port flanges and went from there. I have a build thread on here some where.
Another small tube option is the Patriot Fat Fender Chevy headers. 1.5" primaries and 2.5" collectors. Need the same flange change, but still cheaper than a header kit at around $150. Free shipping for this seller too.
Yes, the two center tubes would need to be shortened to move them apart. But that's still much easier than starting from scratch. The two outer tubes might be very close to correct for a SBF, so just moving two tubes a little and welding a flange would be easy work.
Be glad you're not working on an FE. They only built a bizillion of them, the 427 was a winner in almost all styles of racing but the parts are so damned expensive. But then there is the satisfaction of building one that runs like a raped ape.
yeah . my trans guy ran FE's in his bracket car . lot of factory parts . i have a 460 and a 60 over 454 out of our bracket car. got too many parts for the 5.0 roller already. i'll live with what i have until i find some aluminum heads. right now i plan to build headers from SS tube.