fork height adjustment

I bought a '95 900SS CR. It has a pretty bad head shake on hard braking between 20-30mph and a slow weave in that same speed range during acceleration. Nothing seems obviously wrong with tires, steering head bearings, etc. Anything specific to this bike I should look for?

What about lowering the forks in the triple clamps? Is fork height adjustment a common/useful tuning element on this bike?

Most raise the forks in the triples for quicker steering; geometry on the carbed SS was pretty conservative. Sounds to me more like a damping issue, either front, rear, or both.

have you checked the brake pads and disks?

Have you actually pulled the forks off to check the steering head bearings? Too tight perhaps. Maybe that plus a bent rotor?