I'm 99% sure that is not an HKS Turbo.
I've seen a large variety of old HKS turbos, T300's, T45S's, T51S's, T04S's, etc, and all of them used 6 blade compressor wheels and had Garrett markings, not AirResearch.
If it had a much older 4-bolt DP discharge I *might* believe it was just really...