The D15B VTEC head is indentical to the Z6 head same casting and everything (safe for the cam)... I cannot confirm or deny that it is more aggressive or not, but it does have a different part number from the Z6s... So with this info, slap the D15B head on the Z6 block, and its basically like your just rebuilding your old Z6... So use the same info youd use on the stock D16Z6 engine...