That '54 Corvette exhaust manifold will never work on whatever engine you put it on, sadly.
If you send me a PM with your mailing address, I will provide my address and send you money for shipping it to me...
On a slightly more serious note, I would make sure that you have the correct spring.
Does it look like the slot which the spring goes in has been spread? I would not try to spread nor mash the slot whatsoever.
In your case, you would be better off making a shim to take up the slack. Stainless steel or copper would hold up fine in that environment.
Carl
