You can even fit 750 Zephyr bits to the early motors, they use the same bottom-end, lots of castings and just dress the outside up a bit.
You *cannot* fit an early Z900 / Z1000 motor into the z650/z750 frame. You can however fit the later GpZ1100 or Z1000J motors into the smaller frames. The reason is that the early 900s and thou's had the kickstart casting at the rear of the cases, the later 1000's and 1100's don't, and thus can be squeezed into a 650 or 750 frame. Its a tight fit - I just did a Z1000J motor into a 1980 z750 frame for a Period 5 racer I am currently building. Its a really tight fit, but it can be done. You need to take the cams out to fit the head on, then put the cams in and keep going !
Most of the early 650's, 900's and 1000's use 36mm forks. These can be swapped between models pretty freely. z650 or z750 triple clamps will fit into z900 or z1000 frames, and give you much quicker steering due to the reduced offset. I have used z650 triple clamps in the Black Pearl now for 10-12 years ?? can't really remember when they went in.
Brakes - the early 900's used 6-bolt disc rotors, from the 1976 Z900A4, they went to a 4-bolt pattern. z650's also used a 4-bolt pattern, so disc rotors can be swapped freely between all models that use the 4-bolt rotor. All 4-bolt disc rotors are 295mm diameter, so no worries changing between models. The early 6-bolt rotor is the same as a H2750, as is the early-model calipers. Calipers from the 1976 900 can be freely swapped between most 1000's up to 1980. Rear brake drums / hubs can be freely swapped between H2 and early 900's with a drum brake rear. You will need to change some small items, axle spacers etc, but this is pretty easy.
From the Z1000J onwards, different calipers were used - GpZ1100 calipers can be freely swapped with J calipers from 1981 to about 1983.....the parts interchangability started to decline in the early to mid 80s, there are a lot of external cosmetic stuff that can be changed, eg GpZ1100B1 and B2 and Z1000J tanks are the same, but from 1983 onwards, the models became a lot more *specific* to themselves, in a lot of respects. During the 70's, it was another story altogether !
The twin-disc setup can be done on every Z900. They all came with a set of mounting lugs on the lower RH fork leg, and the RH side of the front hub is already drilled. Getting a disc rotor is easy, but getting a RH caliper for an early Z900 will cost you an arm and a leg. Stick a set of Z1000A1 (1977) forks on an early 900 if you want a twin-disc set-up, its way cheaper.
Wire-spoke wheels - these are freely interchangeable between all spoked model Z900's and Z1000's. The spoked front wheel of a Z650 is also exactly the same as the z900 spoke wheel. The 650 rear wheel cannot be interchanged, the rear drum and hub is smaller than the 900/1000.
Stay away from the Z1000ST - shaft drive model. *Nothing* on these models will interchange with anything else, apart from the barrel/head to other Z1000's. Everything else is different, wheels, brakes, forks, everything.
Found this on another site can anyone add to this ?could be a good resource with the good availabilty of z650 bits.....Paul J..
