usually the differences between a 12 second car and a 13 second car is cam, converter, and gears. Not much else.

Converter isn't a factor since you have a 4 gear.(and I agree with dumping the od unit if you plan on racing it)

509 is good cam for power, but is old school. Keep in mind, you may have to remove your heads, and have the guides cut down, when you get into some of these higher lift cams. A home port may help at the same time. I think your intake will do it.

A decent cam, 391 gears or better, and a set of slicks with a pinion snubber and it should go.

My first pass in the 12's was a 12.48 running a cam similar to a 509( the 440 was 9.6:1 at that time with a set of home ported 452's and stock rockers), with 430's in the 8 3/4, a 3K converter, and a set of 30 by 9 radial goodyear slicks.. i was running a rpm intake, and a 750 mighty demon. FWIW, I still run the same carb and intake into the 11's

As for faster than 12's...just start there. You will find that you want to go faster, and you will get there sooner or later.