I need ideas for fitting a motor to my bike

[Fabian]

But you wouldn't think of motorising a bicycle with anything less than a SickbikeParts shift kit and disk brakes.

 

[KCvale]

It's true. You'll never get an internal combustion engine in that frame.

There are electric motors available where the motor itself is built into the wheel hub.
That could fit. They're fairly popular. But they do have drawbacks.

You could also sell that bike and use the money to buy one with a more traditional frame.
Then you could mount an 80 cc, 2 cycle engine.

That's what I would do, sell or trade that bike for something more motor friendly.

Soft tails (rear shock) bikes can be motorized but seldom direct drive, you have chain length issues as the back wheel goes up and down.
A jackshaft fixes this by using the pedal side drive which is designed to keep chain length the same as the back wheel moves.

They can be done, you just want to use a bike with a rear shock behind the seat post.

Electric is nice too, they naturally hook to the pedal drive.

If you don't particularly care about a rear shock you have way more options.