Re: Will it fit? ;-)
If you want to go over kill, get at least grade 5 steel bolts and replace EVERY bolt in sight. Don't drill "through" the frame for your tensioner, drill into it and just thread in a bolt.
While we're talking about drilling, don't drill through the frame to use the T-style universal mounting bracket, get the U-style. You will need one for the front tube on that frame.
Other things to think about -
Jetting your carb.
Alternative driven sprocket mounting. (clamshell, hd axle kit, disc rotor mount).
Teflon spray the inside of all cable housing.
Personally, I suggest to always remove the cranks derailleur, as they can jam up on the rear right motor mount. I've sheared one off before and since, that's the first thing to go.
As well, it can be done, doing a full ride/softtail motored bicycle, but - I wouldn't suggest it for your first build, stick to a rigid frame.