340 build - last time I "axe" these questions
I'm currently running a 340, 11.1 compression, mildly worked J heads, .508 MP purple cam, Torker and a 650 DP. I think my carb needs rebuilt but it keeps up with the rest of the combo just fine. My opinion? Check out these guys. If I could afford it I'd get a carb from them. Call 'em and they'd probably dial you up the perfect carb. If you want to spend less money, go w/ a 700 DP out o' the box. That's my carb opinion...
www.aedperformance.com
Oh, and by the way. Your combo looks good. The only thing I might consider is a Lunati Voodoo cam instead of your Comp 274. Do a search on these here and read up...after I did it's definately the next cam to replace my single pattern purple shaft!
Good luck and let us know how the build progresses!
Oh yea again...as far as mid-12's. No problemo w/ your drivetrain setup as long as your suspension is set-up right!