Mopar 557 cam

For surely go with the 3.91's and a large cam.

Edit; That Crane listed by Rocco would also don real well.
I have a 66 dart gt with 360 flat top srp pistons and unported edelbrock heads with mopar 557 cam lash set .26 cold into and ex 1.5 rockers. Only 145 cranking comp. 4.1 gear with 28 tall drag radial.weighs 3360 with me in it. Went 7.22 in eighth and 11.55 in quarter with 1.55 60 ft with 10 inch tight 4K flash.If you put against brakes at line 2200rpm it will push.Carb is 750 dp 70 in front with pa and 75 in back with out.I think cam does better than it should.Love it.32 degree timing.
I know your talking about 340 but figure might help you.
Ps intake mI single plane. Good luck Rick