Heavy duty TDI parts are hard to find. The diesel, TDI's even to begin with are built with pretty robust bottom ends, crank, rods, pistons, etc. wise compared to a gas car just because of the stresses they see on a regular basis. However, I believe it is Allard in europe that sells HD TDI pistons, suposedly the VWMS spec units, rods, etc. as well as the overbore kits for TDI's too. 2.0, 2.1, etc. EXPENSIVE stuff though...
There was a guy on Ebay here a while back selling HD TDI pistons. They weren't OEM...some other piston manufacturer, but supposedly they were heavy duty... I thought someone on here was going to buy a set...but that was a while ago. Maybe they'll chime in...
As far as head studs and other hardware goes. Gas studs will not fit, all diesel, 81+ through TDI (with exception the the PD "pumpe deuse" use 12mm head studs. The gas units are smaller in diameter and different in length as well if I remember correctly. Raceware in my book is the best and they carry both the head studs for TDI's as well as main studs...but ARP may have them as well. You'll want to check if the rod bolts that ARP sells are approriate though as when I was looking around no one made a rod bolt specifically for the TDI which has a different style rod bolt than most gas engines. As far as I know, the main stud kits are the same between the gasser and diesels though. Just don't really care for the mexico made ARP stuff and will front the extra cash for Raceware or stock hardware if it comes down to it. Stud and rod kits will also require you to have your block line bored for the stud fitment as well as the big ends of the rods bored to allow the proper fitment of the rod bolts if you go that route.
Maybe thats some help...not sure... good luck...
Joe