DX reborn/Audi pistons

Have dx block to rebuild and looking to reborn to 82.5 mm and use pistons from audi Quattro engine NG.piston no .054107065H as seems to have similar profile to original. Do I need to modify anything ,skim block or thicker head gasket

I'd do a little sanity check on this if I were you. I believe these pistons were also used in old Audi 1.9 engines (same stroke as 1.8) IIRC which had a slightly higher compression ratio (10.5), but not so much that I would be  concerned, unless you are planning on forced induction!. Audi 3A engines had the same 82.5 pistons but longer stroke (2.0 8v) which had the same CR as the DX. I'm assuming that the head gaskets may be slightly different thickness. Otherwise, you should be fine.