Model 7 pistons

I don't actually know, but would have thought if they're handed (ie asymmetrical laterally) that would also imply that they shouldn't be fitted 180 degrees out. For example, a usual reason for handedness is to get the valve cutaways in the right place which would obviously be lost if they were rotated.

But I'm sure someone who actually knows will be along shortly.

My original pistons had larger valve pockets for the inlet valves at the rear. As far as I can tell that's the only difference between front and back. The pockets are diametrically opposite.

The original heplex pistons had expansion slots in them so must be fitted the correct way round.

That is the slots should face the front away from thrust face.

Paul