13 seconds is a nice realistic time attainable with a 350. That being said, it'd be pretty hard to do it with that tbi setup and stock heads. I'd carb that sucker with a Holley 670 street avenger, Edelbrock Performer RPM or RPM Airgap intake, Vortec heads are pretty cheap and flow decently for what you want with some mild porting, maybe this cam
http://www.summitracing.com/parts/CCA-CL12-211-2/ or something similar, stall convertor, and gears. I think that'll get you there. If cost isn't an issue, I'd probably go for a set of Dart Iron Eagles.