you will need to heat it to straighten it out.
warm it up, place something straight over the bend and let it cool.
you need to heat the entire grill to get it to straighten out. so a heat gun probably won't work.
I work in a body shop so heating with a heat lamp would be easy.

you might try putting it in a oven to warm it up. set it at about 250* and see what happens.

maybe try a forced air heater to warm it.

for what 72 RR grills cost IF you can find one. it might be cheaper to buy a heat lamp to straighten it than buying a good grill.