Welcome to the forum. We're glad you've joined us and hope we can help you through your first build of a motorized bicycle.
That might be a tight squeeze and could require some work to get an engine in that frame. Without specific measurements we can only guess but it looks close.
The rear engine mount should be a normal fit but that wide down tube is going to require a special front engine mount. There is a lot of good information here on custom mounting ideas. There are also a few aftermarket mounts that might help. Here is an old thread which might offer some ideas, if the engine will fit > http://motorbicycling.com/showthread.php?t=6427
Good luck and keep us posted on your progress.