Just to give you an idea...most people need at least 260rwhp to get a high 12 to low 13 on street/non drag radial tire. Lots of things go into running a "number". Some variables are track prep,track elevation,driver ability,weight,
suspension,tires etc etc. There have always been the exception to the rules. Your mid 14 is very typical. I ran a brand new 93 GT with all the 5 minute tricks into the 14.0-14.2 range on stock Michelin tires. My 89' with a few small boltons and some sticky tires would pull 13.75--3.80's and my 86 w/89 motor(e cam,all the boltons etc) runs 13.60's. I've raced off and on for 25 years. To get a stockish 302 into the 12's takes a lot of
suspension/slicks/launching at 5000rpm/powershifting/etc. to run in that range you're going to need more horsepower. That is going to take heads/or a power adder. I know you're not talking about making a drag racer. I'm just saying To get any power out of stock heads you really have to know where/what to grind/port. And after you're done you'll still not outflow(or equal)any of the descent aluminums out there. Besides you're going to put some $ in parts for said heads(new springs,bigger valves,seals,grinding/sanding materials,your time,etc). Not worth it believe me.