I purchased a 450 last summer. It had quite a bit of rust but no rust thru. I have taken it completely apart to facilitate repainting. Good thing I did. I found the pully box that mounts to the rear of the housing had an issue.
The pully box has two halves that enclose the input and output shaft gears. The output side has a neck that slides into the rear of the blower housing. I found this neck had cracked all the way around. I'm not sure if my welder can repair it as its cast. The other issue I found was the arm that supports the shute control was cracked down near where it mounts to the blower housing. I only found it after I stipped off all the paint. Took it to my welder yesterday. It's good as new.
Moral to this story is you can find and fix a lot of problems when you tear it down and strip away the grime, rust, and forty years of paint.
Good luck with it.
