Which heads wpuld be better?

Why not chunk the 318 and put a 360 in there? A friend of mine has a 72 Duster full interior 360 "J" heads + aluminum intake + 750 Holley + 292/.509 cam + 1 5/8 headers + auto/2500 stall conv.+ 3:91 gears = 12.58 sec. 1/4 mile
Glad to see you chose the right brand...70 Swinger.

Chevy kids
Ford boys
Mopar Men
When Mopar Performance used to be Direct Connection they used to sell a really cool shirt that read: Mr. DC says"Real men drive Mopar". Wish I still had one.

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68 Dart 2 dr. ht. 318/auto soon to be 360/4 speed....68 Dart 2 dr sedan 440/auto/4:10's....74 gremlin 360 (Mopar not AMC)/auto/8 1/4 rear w/3:92's (a Mopar in Gremlin's clothing...lol.)