Ok, let's set the record straight about modern Z06 here.
The C5 Z06 came only with LS6 engine (5.7l). In 2001, the power was rated at 385 hp and in 2002-2004 model years, the power was rated at 405 hp. A C5 always has a 5.7l V8, whether it's an LS1 (345-350 hp) or an LS6 with updates throughout the model years. BTW, LS1 and LS6 actual displacement is 346ci.
The C6 line up is a bit more complicated. A C6 Z06, so far, has only been given the LS7 (505 hp, 7.0l). A base C6 in model years 2005 through 2007 has the LS2 (400 hp, 6.0l). Model year 2008 through current has the LS3 (430-436 hp, 6.2l). The ZR1 (C6, not to be confused with the ZR-1 which is a C4) has a supercharged LS3 dubbed the LS9 (638 hp, 6.2l SC). The supercharged 6.2l in the current generation Cadillac CTS-V is called an LSA (556 hp, 6.2l SC) and it's considered a detuned LS9.
Recently, I looked into V8-converted Kappas and I found I could not justify it. It cost about the same as a C6 Corvette after everything is said and done. The power-to-weight ratio is similar to a C6 as well since the conversion adds weight and puts it right to a C6 weight. A couple other shortcomings are the weaker differential/final drive and the fender wells of a Kappa can't take wider tires. And if the aim is the Z06, it will be very hard to match its aluminum frame, composite body panels, and magnesium cradles/subframes.
That said, I still want a Kappa with an LS7 or LS9, I just need a lot more money to overcome my common sense. Yes, I fully understand the saying, "more money than sense" ...