How to straighten hood?

If you can find another hood, replace it. Once they are bent they become flimsy. Resistance from the hood hindges cause them to bend again in the same place.
Yes the older hoods are better made than new cars but those hindges are much stronger than modern lift struts too.
I've seen oil change monkeys grab a hood at a corner instead of center when closing and buckle a hood that previously had nothing wrong other than stuborn hindges.
Another point to consider is the view from the drivers seat. We cant even see the hood on modern cars from the seat. You will always see a hood repair from inside a classic.
Just points to consider. Good luck either way