bellows are broken
A big problem that plagues many of these types of Polaroids is the dreaded busted bellows.
This particular camera had a bulge or two from bad bellows. They must be replaced.
bend tabs up
If your bellows are ruined in any way, you MUST replace them.
If you can find another automatic Polaroid like yours, awesome.
Preferably take one from a cheaper one than the 450, one that is worth losing. Check the lens plate to make sure your 4 screws will line up with your new bellows.
Remove these 4 screws now and save them for later.
The spring arm sits within a slide held to the lensboard with a screw and by a small bolt, red arrows.
Removing the bolt will cause a metal rod and washer to fall out.
The top and bottom are connected by this metal rod, unscrewing one or the other will cause both to fall out.
Now slack, you can unhook the spring too. Save these parts and remember the order in where they go. 
Now the entire lensboard and shutter assembly is free and can be worked on.
remove 3 screws
Start with removing the 3 screws that hold the 2 halves of the shutter together.
The shutter cable has 3 screws, only one needs to be removed.
But remove all three anyway.
The top and bottom are connected by this metal rod, unscrewing one or the other will cause both to fall out. Save these parts and remember the order in where they go.
Now slack, you can unhook the spring too.
remove 4 screws
Inside you will find the circuits we’re ditching.
2 small screws and 2 large screws hold it all to the housing.
Toss the circuits.
Unless you plan on keeping the original faceplate, peel it off as a stencil for later.
Remove parts by simply yanking and twisting all the parts you see in the front.
The lens and electric eye pieces can be unscrewed.
Three screws and the stuck label on the top, hold the lensboard together.
First was the shutter release, the last two are on the back.