3.4 to 3.6 using 997 3.8 99mm pistons
 

Im doing all the homework I can into doing a 3.4 to 3.6 engine conversion.

Ive found the Wossner pistons and they list all the speca of them (OE specs)

As you are probably aware, to go to 3.6 from 3.4 requires 99mm bore. The 997 3.8 has a 99mm bore.

Can we use these off the shelf pistons for our 3.6 big bore engines?

3.4 996 spec

11.3:1 CR
15cc bowl in top of piston
32.3mm compression height.

3.8 997 99mm pistons

11.8 CR
13.8cc bowl
33mm compression height

out of interest

3.4 987 S
7.8cc bowl
11.1 CR
32.3mm compression height.

Does the 3.4 996 engine , albeit with a 99mm bore, accept thr 997 S pistons?

There's also another measurement, although I forget the proper medical term... It's the measurement of wristpin centre relative to the piston top.
In some stroker motor situations, stock pistons can extend out of the bore @ TDC without a specially made piston set. I'm not sure if it applies in your example, but it did back in the day building a 347 stroker out of a Fox body Mustang's 302 V8.

I think the measurement you refer to is the compression height.

who is doing the work on crank case from .34 to 3.6?. I plan the same thing in the future

See if you can get any insight from what parts LN would sell to do this. We know they sell (and Flat6 uses) parts to alter the displacement of 3.2 and 3.4 motors.

I'm in the UK and have sorted a machine shop.

I know Mr Raby uses custom JE pistons.

Piston pin height is the simplest term. When you are "stroking" a engine for max swept area volume & thus max displacement you install a crankshaft with longer "throws". Porsche did this in 2002 with the new 3.6L engine. To offset the additional length of the crank stroke the 3.6L has shorter rods & revised pin height pistons.
In the OP's case the pin height will be off & the piston valve pockets & dome will be a different design. This is one of the reasons LN designed the new pistons for this application.

deleted -- had my logic backwards

That's the term I was hunting for. I knew someone in the brain trust would be able to say it, even though all I could manage was to charade it out...

The learning curve with this is 90 degrees.
Cylinder preparation and ring pack are the main considerations, as well as running clearances.

Its all in the combo, not just a bigger piston, or a forged piston.