Cylinder/piston interchangeability

[WERK I]

Hi Porschephiles,
I am relitively new to the Pelican forum and have enjoyed reading the posts and am impressed with the amount of knowledge available to the masses.
I have an 85 factory slantnose turbo that I am going to be doing a tear-down next week while I have the engine out.
The engine is a 930/66 (3.3l RoW)series that was modified with an Electromotive crankfire and twinplugging. The PO replaced the pistons and cylinders about 20K miles ago. The thing that has me baffled is the pistons/cylinders are from an early C2 turbo(written in build sheet). When I had the alternator out last year, I noticed the cylinders have the fins all the way around.
My question is; didn't the early C2 turbos have a differant cylinder machining at the bottom to work with the new base seals? Also,
did the head gasket design in that period change as well? It would seem that if this true, then the case and heads would have to have been machined and yet, I see no record of it on the engine build sheet.
Thanks for all your advice in advance. Great site!!

Dave