There's going to be a law of diminishing returns that needs to be considered when deciding whether or not to go turbo KL03 or turbo KLZE.
A KL03 with a blower can safely produce something close to 230HP at the wheels when running 7-9PSI, assuming the engine is sound mechanically. With a 9.2:1 compression ratio, the engine is fairly happy with boost levels this high. The ZE, with something like 10:1, may not like that much boost and, because boost may have to be moderated, its output may suffer because of it.
I've not yet seen dyno plots of a KLZE running a turbo but I suspect it's probably not putting an additional 35HP, over and above a boosted KL03, to the ground as safely as the KL03 is producing its output. The higher static compression in the ZE means it has a higher propensity to suffer detonation, which will ultimately limit the amount of boost you can run before hurting stuff.
Also, while the ZE has constructional differences from the 03 but they are limited, in the reciprocating assembly at least, to different pistons (for increased compression). AFAIK, the ZE uses the same skinny connecting rods and the pistons are still cast (someone correct me if I'm wrong). Cast pistons are not ideal for boosted apps and with compression that high, there's a very real chance of breakage.
So despite the fact that the ZE is the "performance" engine of the KL series, it doesn't automatically follow that it will make
that much more power when boosted, reliably, over a boosted KL03. And it also doesn't mean the engine can be boosted to 15PSI out of the box.
If it were me, I'd stick with the KL03, put a turbo on it and drive it sanely while I put the $2200++ a ZE would have cost toward the purchase of "real" turbo innards for the 03: steel aftermarket rods, forged slugs, cylinder head O-rings etc. Oh yes...and an LSD
