How to bend Unknownbbq hinge for WSM 22 for better curvature fit

Guessing you're having issue with one or both of the plates being flush to the WSM for screwing on?

Could try what they recommend for the door - a paint can.

Do check your alignment though with both pieces. That is, mark the drill holes with the hinge flush to both the lid and middle section; like it would be when in operation. I ended up with a pair of extra speed holes because I didn't.
Mine came in bent or rather pulled out of shape from the welding heat.
I posted a pic of mine yesterday.
Does yours look like mine?

I don’t have much for tools here at this old house.
I do have a old antique wood worker vice.
I opened it up about 4-5 inches and laid the low section of the radius in it then used a wood block as a center punch so to speak and struck that with a crappy hammer.
I‘d hit it once or twice then check for fit.
Towards the end of the repair I had to bend last inch or so of the end sections to get a proper fit so I closed the vice on an end and hand pushed it to achieve the correct radius.
It is important to do a little tweak at a time and check for fit often.

Mine ended up looking like nothing was ever wrong with it.
I‘m interested in knowing how your situation works out.
Call Jason and tell him that something isn’t right. He is a great guy but, it’s kind of important to let him know that there is a QC issue.
He was very helpful when I decided to put a hinge on the 18” kettle on my “Overperformer” he does need to know what it’s going on just because they are a “little” different.