I`d contact the last owner and ask what was done to the bike.
It would be good to know if the engine is still the original one or swapped for an ST2 engine but should be easy to identify as the 907ie engine is all black, the ST2 has silver cylinder heads, grey belt and engine covers and the clutch slave piston is different as well.

If it is a 907ie engine it would be good to know if a big bore kit was installed or if the original cylinders were bored to fit larger pistons. Then it also would be interesting to know if these parts were aftermarket or from a ST2.

You can go back to original cylinders/pistons (not knowing if the FBF chip is for a 944 kit) or have your new cylinder modified to fit the old piston. Looking at the grey areas on your old cylinders though I wonder if you`d also need new piston rings then.

I'd buy used ST2cyls & new rings to both pistons
and reassemble.