I have a 1989 ZX-10 (I'm the original owner) and 04 ZX-10R, the only things similiar about these 2 bikes are the ZX-10 other than that completely different.
The 88-90 ZX-10 was tested to have 115-118 hp, 65 lb of torque and 163-165 mph top speed now these numbers depended on the mag doing the testing at the time. My paticular 89 dyno'd at 118 rwhp and 65 lb of torque stock. Going with some minor mods like full exhaust, ing advancer at 3 1/2 degrees, degreed stock cams, K&N filter and Dyno Jet Stage I kit it dyno'd at 130 rwhp and 71 lb of torque. With some major engine work I was able to coax 150 rwhp and 80 lb of torque.
With the weight and length of this bike most modern sport bikes will run circles around it in terms of performance and handling though that does depend on rider skills. With the right rider the ZX-10 is still a lot of fun to ride. Even having my 04 I still enjoy and have fun riding my 89 I just ride it a little differently than the 04.
for non OEM body work, haven't ever seen their stuff for the 88-90 so not sure what quality/fit it is. You can still get factory pieces but they take a while and you will pay.
If you want more info/opinions on the ZX-10 shoot me a mail at firstname.lastname@example.org
and I'll do my best to help you out.