340 cam in a 318

I had the aforementioned LA 318 in my Dart with 3 91 gears, and a 4 speed. Everything stock LA except the intake, cam, 4 barrel, headers and 2.5 inch exhaust. I ran it on the street and it was fun but it ran about as fast as my bone stock 86 Mustang GT convertible which is a 15 second car. Now I hear tell stock 340 darts can do 13s so...my 340 Dart is going back together and maybe one day I will see, this year Ill be running my Mustang again at test and tune night...my Mopar is more of a resto than a race car...still has 14 inch E 70s on ralleys for example. I mean yeah you can scratch your head and dick around with 318 LAs swapping pistons grinding ports but why? get a LA 360 or any magnum (for the heads) and build it and save yourself some time.