For mine I built a small frame that fit over my wheel, the engine attaches to this, spidle direct to the engine. Then I made a clamp that attached to the frame of my bike. I have a few other modifications, but nothing permanent to my bike.
Check out some of the pictures in this forum to get ideas.
I've put 2 pics attached. First is of my clamp. I've redone the clamp and now use a piece of right angle and hinges rather than the old hinge with the all thread. It works very well. Next shows the engine on the bike.
After I get to this point in a build I use a gate spring and turnbuckle to give me adjustable tension on the tire. Engine lifts up and down with a brake lever, cable and 2 pulleys. Hope the pics help. This section of the forum has al the info you need to start.