The 5.3 can be bored to LS1 size, giving you an iron block LS1. My 2000 6 speed 3.42 gear factory stripper Z28 ran 13.30's with just a airbox lid when it was new. With SLP loudmouth, thermostat, filter, and sticky tire it ran 12.80's. I suspect it would still run those numbers with 127,000 miles on it. (I drive it every day) Point here is it's just fine to use a 5.3 to do a swap. You could upgrade to 5.7. or 6.0 later.