Originally Posted by KiwiStarChief
However I just wonder if it would be easier to slot the bolt holes where it bolts to the firewall by the 3/8", and drop it that way.
If you can access your hinge-to-firewall bolts somehow, with the hood already closed and latched, you could loosen or remove them and see if that corner goes down. If it does, slot / shim it so it sits in the right spot when bolted tight. Looks like that may put the washer out over the edge of the hinge but I bet you can deal with that if it solves the problem.
Since the guy with the Chevy has similar drama, this could be an inherent issue present on lots of cars made then. But, the original poster says his bounces a little going down the road. If yours also can be pushed down once closed... sorry, men... worn hinges are a prime suspect. By the same token as the above suggestion, unhook the spring and see where she sits. If it lays down then, great. But if it can still bounce, thats hinge slop.
To the OP, just be careful when affecting latch closing. I have seen too many cases where a guy gets his hood closing "nice" and needs a hood, windshield, and roof the next week. A bit of effort will be required to close a properly adjusted setup, and any movement possible when closed (such as when side bumpers are left out) is a time bomb.
In a nutshell, do whatever is necessary at the firewall. You are probably compensating for hinge wear by doing so but no matter. Its old enough that modification might be required to make things work and fit right.
The top side mounting arrangement certainly is a circus on the Pontiac anyway.
Only other tip I can think of is to be sure the right front hood height bumper is making contact.