Is the (standard) clutch plate the same for an irs and swing axle beetle?
If I am looking to swap engines on my swing axle beetle, and the new engine came out of an irs beetle, will I have to swap the clutch for the current one?

depends on if the beetle was 12v or 6v. IRS would all be 12volt and have a 200mm clutch. Swing axle could be 6v 180mm clutch or 12 v 200 clutch.

Then there was the 6v T3 flywheel with a 200mm clutch. Confused??

Easiest way is to measure it. :thumb

both are 12 volt, so both should be 200mm?
so if they are the same size they should be compatible otherwise?

Yep they should be the same. Pay to measure tho. The only other difference is the pressure plate. Could be either the 3 lever type or the diaphram type. You can tell the difference easily. This will determine the type of throw our lever arrangement on the gear box.

OK, so if the clutches on the two engines have different pressure plates, then I will need to either swap the clutches or change the throw out lever in the gearbox?
Which is easier?

The pressure plate!!!!

Yup, the pressure plate for sure.