I had an LT4 vette with a tune, corsa pipes, 4.10-1 gears and an airbox and it ran like a raped ape. While I have ridden in (not driven) a modded WS6 01 T/A, I have to say the LT4 didnt feel like it gave much up. Remember, the LT4 was underrated by GM, it was more like a 365hp car than a 330hp one, underrating was done to keep new LS1 Vette buyers from feeling robbed.
Not bagging on the LS1, but cost up front is definitely higher. Opti is around $300, not too high, although it is some work. Like I say, gears and an LT4 hot cam and you are talking 400hp with a tune on an lt4 car, maybe 360ish on an LT1. Bilstein shocks on my buddys ws6 car stock....just set up better out the gate. To take a non-WS6 car you are 30hp down, may be stuck with 2.73-1 gears with no posi, etc. To pull 30hp out of the car, bigger wheels, 275 section 17" tires, sway bars, bilsteins, a posi unit,gear swap, etc. It is a pretty good package, and I would say you are talking a few grand to re-create it (tires, etc included). To each his own though, but I would rather start with a better equipped car right out the gate. Once again- much love for LS series engines, but when you are trying to get a hot rod for 3 grand, the upfront cost seems critical