Yes it looks lower at the front, you could tighten up the end bolts on the rear spring a tad, that would lower the back and lift the front, but it may still not be correct, because at the moment from the pic the back looks good, NCRS and looking from the pic I would want to back track on what part numbers were used for the front springs and then there could be an error in the info - May be the wrong springs used - Where do you go to find the correct source info for spring rate spec 66 427
www.gmheritagecenter.com (drop them an email) also Scott at Corvette Kingdom should be able to help you with the exact correct springs
Worth dropping the back a tad by tightening up the end bolts - quick and costs nothing before looking further.
As you may know correct and best stance is always a tad lower at the front, but just a touch
Looks good and as it is NCRS good to keep it original.