I purchased 2 cast aluminum Corvette valve covers for my early 283 Bel Air 2 years ago. I just got around to trying to put them on. They are a GM Performance product. They do not fit, and Pace Performance where I bought them will not take them back because I painted them (Aluminum color), and it has been 2 years. I would imagine that a lot of people buy parts and cannot put them on right away due to long restoration projects. Has anyone heard of the staggered/offset bolt pattern being off by half a bolt distance so that only 2 bolts go in, and the other two cannot go into the head? They are for my older engine, and are sooooo close to fitting, it is frustrating. Both Pace and GM have basically told me to suck it up, I gave them money for crap. The paint issue should not be an issue since they cannot be resold due to not fitting anyway. The time issue was just a hunk of metal sitting in a box on my shelf, no degradation there. So two points here, has anyone heard of this problem? Are there differences in heads besides the offset and non-offset holes? The other is I would carefully consider buying from either of these companies.