How to measure cam base circle 1983 gpz750

1983 gpz750 non turbo just not sure on how to measure the cam base circle

Just to clarify, only the exhaust cam on the 83-86 Unitrac zx750's have a smaller base circle. The intake cam has a "normal" base circle exactly the same as any other kz750 or kz650 intake or exhaust camshaft.
So the only way to accurately measure the base circle or lift on these sort of cams is with v-blocks and a dial indicator. You can't just use calipers and measure across the cam lobe 90° to the actual lift as the ramps for the lift start before then. (You won't get an actual measurement) You can zero the dial indicator to the bottom of the base circle of the intake cam and then put in the exhaust cam and see the difference in lift on the indicator.
Or....do what I just did. Measure the width of the base circle of the Intake cam with calipers 90° to the lobe...or.... measure from the top of the lobe to the bottom of the base circle, then measure the exhaust cam in the exact same spot.
The exhaust cam will measure roughly 1mm less in width or length if it is a small base circle cam. Not very scientific, but it will tell you if you have an actual 83-86 zx750 exhaust cam.
I simply can't remember what the actual scientific factory base circle numbers are right now, but if you have v-blocks and a dial indicator you can find out.

In addition to the methods Daftrusty suggested for differentiating between cam types, ...

If it's still in the bike, I think you can measure the peak bucket displacement with the depth gauge of the caliper and add the lash measurement. Then subtract that from a caliper measurement of the full height of the lobe from point to heel.

It won't be as precise as placing the camshaft in V blocks, but should get you close. The main fudge factors are the lash, and if the camshaft moves in the bearings due to uneven spring tension.

I think that's a way to do it.