Factory shock absorbers differencies, info needed?

Could somebody help me, please, with this specific info: what´s the difference between the front shocks for 20VT and 20NA (or 1.8L)? Is it only to stiffness, or there is also difference in the physical dimensions? How it goes with the rears?
...as I´m trying to deal with parts dealer, who´s not very sure what he is dealing with
Thanks...

...so, according to the Boge/Sachs catalog, all engine versions share the same rear shocks, 20VT and 16VT share fronts, and all NAs also share fronts, so there are two models of front, and one of rear. Can somebody confirm?
...unfortunately no data on the hardness of the front ones.

It may just be the Hub mounting bolt spacing that differs, the 16v has a smaller distance between bolts than the 16vt and 20vt.

Not sure on damper internals though?

...and taking apart the distance between holes, they appear to be the same externally? The turbo versions shocks have to support higher weight and forces obviuosly, so this should be for some safety and/or maketing strategies.
Well, the case is that have found small factory with some history and experience in motorsports, very interesting product range, but which, somehow, doesn´t support the turbo versions shocks. They´ve offered to upgrade my existing set for a modest price, but that idea doesn´t excite me, they use very similar to Koni´s method... simply preffer upgraded new ones So, will try to convince them to make a set, but need to know the certain difference, at least in dimensions and montage...