81 to 85 kz gpz 750 cam swap

I have a performance cam from a 81 kz750 will it fit the 85 gpz 750 head?
don't care about tack drive
But was told they have a different base circle,is there a way around this?

I don´t know the correct numbers for the KZ750/GPZ750 base circle but you need thinner shims (0,30 - 0,40 mm) to set the correct valve lash.

If you have stock pistons in that GPZ motor you may end up having collision problems with higher lift cams, if the cams sprockets are slotted you can eliminate the piston to valve collision with careful adjustment. Most higher lift cams are for motors with aftermarket pistons where the valve pockets are cut deeper, there is hardly any valve pocket on a stock cast piston.

I am NOT an expert, but I thought it was the later year engines that used the smaller base circle.  

Good chance you can find the info you need in this link... members.tripod.com/gpz_rider/technical/FAQ2000.htm

 

Using Arias 750 Pistons
cut outs are all fine 
Just came across a road racing cam from an 81 kz 750  just wondering if I will have problems putting them in a 84: head

If the cams came out of a 1981 750, then they will work just fine. 
1984 on up gpz’s use a small base circle exhaust cam anyway, so all you have do is re-shim. As another member mentioned, using slotted sprockets and degreeing
in the cams is best. Performance cams are not designed to be bolted to stock sprockets and plopped in a motor. Every motor is slightly different (decked head and cylinder surfaces changes the distance between the crank and cam sprockets which affects the index of the cam chain and thus the cams.) 
If you can, post some pictures of the cams so maybe we can identify them further.   

With slotted sprockets you can start in the middle position (stock) then move in either direction depending on interference (valve with piston pocket) Even if you don't have a degree wheel you can adjust the piston to valve clearance and check the clearance with some plumbing solder (.060" intake/,080" exhaust) Just make sure you have good clearance on the shims before proceeding with adjusting the cam timing, you want to have .006" minimum clearance in case it closes up a bit when running.
Stock 650/750 sprockets are easily slotted with a 1/4" carbide bit in a Dremel tool, it takes a bit of time but it works. They cannot be slotted using a file as they are hard.