[Mr70]

Z15 is 454 LS-5.....No 454 LS-6's assembled @ Oshawa Canada.
Z25 is 396 L-34.....No 396 L-78's assembled @ Oshawa Canada.

I've never seen anything under a drivers seat,just a CON-VIN,(not a full VIN),on the rear rail behind the back bumper and yes,the body would have to be off to see it if there.