The Z/28 has a 505hp LS7. Completely different setup, but there's just not a big market for it since there's a 580hp, more streetable variant for the same price.
The ZL1 shares the same LS3 with the SS/1LE (and Corvette) but with a blower strapped on. The 1LE is basically everything a ZL1 is, minus the blower - sway bars, suspension, 20" wheels, 285 F1 tires, brembos, interior bits, air-to-liquid cooling, trans cooler, half shafts, fuel pump, Tremec TR6060-MM6 with 3.91 gearing (normal SS's have a TR6060-M10), dual-mode NPP exhaust, and um.. probably some other stuff. All the same between them. One exception is the 1LE has only the front wheels/tires off a ZL1 on all her corners, as the rears are a tad wider on the ZL1. The plain-jane SS comes with none of these.. so, not bad for a $2500 upgrade to a 1LE if you're into driving hard.