You're going to need to post pictures of the axle stamp and the date code on the center section. Also, 4 leafs isn't definitive proof of a Z28. 4 leaf springs were used on non-Z28's as well. The UH radiator was also used on the base V8 327 engine, so again, no definite proof, especially since I believe these are being reproduced.
Post a picture of the engine pad too. Make sure you remove any paint with paint remover and DON'T use anything abrasive. If it's the original engine, that'll tell you exactly what you have.
Ed
