340 in 63 dart

As stated, Doug's, TTi's, fenderwells. Not mentioned are Spit fire shorties. You didn't mention if you had power steering, if you do and you want to keep it, that cancels most choices.

I personally have used Doug's and know others who have used the Spitfires, they work.

Get in a pinch and you can use the 64 to 66 273 manifolds, though the above selection would be a little better.

Good luck!