I've got one like that and shelved it until I've got the time.
You'll need an actual heat gun and heat up the block for awhile to expand everything. Then you'll need to get it on the box fast! Starter box batt better be fully charged too. Mine ran the dang wheel right off my starterbox and I was pretty mad so put my other engine in!
Or if you have a pullstart you can use the one way and start it with a drill. It's really the only way I've been able to start overpinched motors. The one I have now doesn't have a pull so I'm going to mount it to a board and start it with a drill using a socket on the flywheel nut that will barely be on the nut. I wouldn't advise this though unless you feel fully competent to do so and don't hold me responsible if you break a finger or two.
Did osrocket pinch it for you? If all else fails you can send it to rayaracing resizing and he'll "unpinch" it for you so it's not so tight. Just google search rayaracing and shoot him an email. He's about 20 bux and does a great job. Osrocket does great work too, but I would only ask him for a very light pinch if having him do it again.
If you decide to scrap the motor, shoot me a pm and I'll take it.