I had a friend that has a 66 long box with a stock LS 5.3 with a 4.10 gear. I had my 90 GMC shorty with a stock 350 vortec with a stock marine cam. Both were 2 wheel drive one with a 200R and I with a th350 and a 3.42 rear gear. BOTH truck ran almost the same ET. 14.75s and the weights of both trucks were almost the same 4,425 lbs. with drivers. My take is the LS looks nice, but will take a butt load of money to get it to run. For half the price of the LS upgrade you could stroke the vortec block and upgrade the valve springs and add a Comp. 282HR cam. That combo in a 80 cutlass with DR and a small converter and street driven to and from the track would go 11.86 at its best pass. This is what I had in that motor for money. $200 for the 350 truck vortec , Clean and hone the cylinders and put in new cam bearings. Stroker kit was a $800 balanced kit from Comp Products with the dished pistons to make it a 9.5-1 motor with the 64cc heads for pump gas. Comp cam from $150-300 for a regrind or a new cam, I used the regrind from ebay. Comp bee hive valve springs and retainers $225 also from Comp Products. Thats the motor I built for the 80 cuddy. My take on a stock LS and a stock 350 vortec truck motor, both make about the same power. Add a bunch of money to the LS or put a good upgrade cam and springs in a 350 vortec and both will make good power.