Moey,
Welcome to the forum. We don't allow new members to post links. You'll need to become active on the forum. It just takes a few posts.
The bike you linked to would not be a good candidate for an in-frame engine due to the rear suspension. It could be motorized by using a rack mounted chain or friction drive system but the frame of that bike and the swing arm rear suspension will not allow an engine to be mounted in the frame. There is no room for an engine and the chain tension would be a problem for you.