The Autech GTR sedans run a BCNR33 (Kai) chassis code, not ENR33. They weren't like the Autech 260RS Stageas that ran the same chassis code as the regular wagons.
Saying that an Autech GTR sedan is a dressed up ENR33 sedan is no different to saying an BNR34 GTR is a dressed up ENR34 coupe - they're completely different cars. Autech did the work because Nissan couldn't justify modifying their production line to do the rear guards or the rear seats in GTR trim, I imagine all the rest would have been done at the factory - it's just a different combo of factory parts for Nissan.
Like I said earlier, if anyone wants one, I can make it happen. I've had a couple of workshops say they reckon they could get one complied using a combo of evidence from the R33 GTR coupe and the R33 sedan.