I'm not trying to be confusing but I guess I am to a certain extent. One thing this whole idea hinges on is the interpretation of what "stock" means. Techically it means exactly as it came from the factory but you won't find many truely stock trucks like this and you also won't get a concensus on what stock really means, for some it means the engine is untouched but for some it could mean that only the shortblock is stock and they could have any number of upgrades bolted onto it, so be prepared.
The other thing is where these engines make their torque, your improved 5.0 certainly could make 350+TQ but it'll be peakier than a 5.8, so while a stock 5.8 only makes 340tq it has most of that available from 2000rpm, so the bigger motor will have an advantage out of the hole and at the lower rpm range of each gear... all else being equal. This is the basis for the saying "there ain't no replacement for displacement", and it holds true regardless what numbers an engine simulator throws at you. So all that said, yes you can beat a stock Lightning or old Silverado with a built 5.0, you're just going to have to better those trucks in the HP and gearing dept to do it.

 

wow well thanks for this thread with all the info im trying to do the same but with a budget. starting with the exploer gt40 heads from the junkyard i do plan on 4 10 rear what factory truck have them and are they the same quality as aftermarket or close? i know alot of my part i will have to buy new but just trying to get the most out of the junkyard as possible as to were its alot cheaper for me. nothing has been done to my truck yet all the parts i do have i set aside for when i do tear it down and replace all at once but i think it a light truck to work with and with the appearance of it i always get people trying to run me on the street and im tired of not performing aswell as others i have a 94 flareside 150 with the mark 3 package and body kit ext cab if you go in my garage somewere you can see it. it does ok stock but like everyone here i need more hp and tq

 

A GEN 1 L will run 15.6-15.2 cutting 2.3 to 2.1 60's in stock form.

I've seen many races lost in the first 60 feet because of gearing and/or running stock a converter. If you build you 302 as if it were in a Mustang, I'd suggest you change the gearing and/or go with a higher stall converter if it's within your budget.