RHE7, eh?
Well, according to Isuzu, both the IHI-RHC7 and the IHI-RHE7 are used in the 600 CI diesels and put out about 615 ft-lbs of tourque at 1400 rpm in that application.
My guess would be that the E7 has a slightly larger exhaust wheel or some small change like that.
What is the cm of your exhaust housing?