Which newer motor

Tooling around with the idea of putting in a new motor off a newer wrecked kawasaki. I found a zephyr 750 wrecked and the motor looks almost identical to mine.

Have a look at my engine setup, will the 750 engine haul any better? From my research I understand that the zephyr is based off the GpZ750 block with even stronger internals. Of course I could be wrong, I would think 20 years of engineering would bring some advancements.

I can't afford much more than just the bike right now. But If I were to modify what would be the first step, GPZ750 cams?

Based on and looks identical to me are two totally different animals. All it takes is an 1/8" for something not to fit at all. Metal parts don't bend out of the way easily. That said almost anything is possible with enough time, money and sheer bull headedness. You will have to get exact measurements of the Zephyr engine and match those numbers up to the engine mounts on your 650. I have seen a GPZ750 motor in a 650 frame with Z1R body work, so it is at least possible. An engine based on another may not actually have any parts that interchange. A good 4-1 pipe, pods, aftermarket electronic ignition (if stock is points) and degreed cams can give a noticeable boost to any bike. With minimal work and money.

Is the KZ650 with the GPZ750 motor on the forum? I'd like to know his experiences....

I think there is more than one KZ650 with a GPz750 motor on the site.

I helped my nephew install the GPz750 motor in his 79 KZ650SR and it's still here. Easy install by the way