Id have to look through the old Japanese HKS catalogs but I this is the HKS T04 upgrade. Not unlike the TO4E upgrade but that turbo bolted onto the factory manifold whereas this had a dedicated T4 manifold and external wastegate. As far as power is concerned these were upper 400's low 500s capable with proper tuning.
Update: I was able to remove the entire exhaust side from the motor, here are some pics. The plan is to refurbish/rebuild as much of this turbo kit as I possibly can. Anybody know where I can find this exhaust flange for the hotside?