Gas in Oil, what next?

I bought a 1982 KZ550 as a first bike and restoration project (mistake lol), it ran fine for 2 years though extremely rich. it used to leak fuel from the carbs but i rebuilt them. I let the bike sit all winter and when i took it off the rear stand it pissed gas all over the floor. drain the oil to find it full of gas. gas tank halfway emptied.

What's the work I'm looking at to fix this? From my research I found that I might have to look at the petcock (vacuum), the piston rings, the floats in carbs and my valves. Any insights?
Since the gas was leaking out from under I assume I'm going to need to change a gasket but i couldn't find the source of the leak, it was on the left side of the bike. 

Thanks.

If the petcock isn't shutting off (do not leave in the "Prime" position) the tank will "syphon" through the carbs - some will leak out of the carbs into the airbox and some will leak into the motor and drain down past the rings. Potentially all it needs is the airbox cleaned out, the oil and filter changed and the petcock issue resolving

Look up how to do a clear tube fuel level check. You probably have one or more carbs with a bad float valve, allowing the bowl to over fill. Also fix or replace the petcock. Most likely there's no permanent damage.

You username is very fitting for your issue! sorry i had to...

On a serious note, both of them are right. Something in either the petcock or carbs is allowing fuel to seep out of the petcock into the carbs and down the airbox and through the crankcase breather.

For the petcock, like wookie said, it could be the o-ring on the diaphragm or the o-ring for the handle for the petcock. For the carbs, like ckahleer said, it could be your float bowl height or a stuck float valve.

The float valves are not designed to hold back the fuel indefinitely.  That's why the OEM's invented vacuum petcocks; they shut off fuel flow when the engine is off.  As already mentioned, check the petcock, and don't run the bike in the "prime" position for any longer than necessary.  

Second step, after changing the oil, is to check the petcock function.  Again, no fuel should flow unless a vacuum is applied.  Sometimes when a vacuum petcock fails, fuel flows backwards, down the vacuum line and into the carbs that way, so check that as well.

Check/fix the fuel tap.
change oil and filter.
DO A COMPRESSION TEST. if its been running with fuel in the oil then you've been washing the bores not lubricating them. Your top compression rings will destroy themselves in VERY short order if thats the case.