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Ok ,i have an 85 and an 86 cylinder that i want to install on my 99 bottom end.My question is do i need a cylinder spacer or just the thicker head gasket?And also would the 85 or 86 cylinder be better for mid to top end power?

The old cylinders will work with no different base gasket, or rear stud change. The sleeve diamiter is smaller so there will be a little more crankcase volume which shouldnt hurt. Use the old long reed in the jug and depending on what chassis i'd probably reccomend using the plastic insert in the reed and cutting the ears off a 89+ reed boot so the carb is further from the spring.
The thicker head gasket is only relevant to the head, 85-86 have small chamber, 87-88 mid, and 89+ large, the 85-88 head gasket is thick, the 89+ is thin, 87-01 is almost the same chamber volume when used with their stock gaskets, but way more squeeze when 87-88 head and 89+ gasket

With an 87 cylinder with a thin head gasket the piston will tap the cylinder head.

Don't ask me how I know this.

which head?
I'm running an 86 crank, cometic thin base gasket, an 89+ thickness cometic head gasket and and 87 head on an 86 jug with .055" squish or something. all stock, just a nice combo

I have a 99 crankshaft [long rod]in that bottom end but the 99 cylinder is on the last bore.That is why i need a diffrent cylinder.I thought i read somewhere that you need a spacer plate for the older cylinders. I really want to build a high speed desert motor.By the way the motor is going into a gen 4 450.

You only need the spacer plate when you put a long rod in an early engine, because they have ashorter crankcase hieght.
A 99 bottom end is fine.