You could be right, not sure.
I have heard ( among other places it was in dutra's book, and
@my68barracuda has mentioned this in the past as well.... The 81+ slants had a cast iron pump which was slightly higher vol than the 80-older alum bodied pump. 7/8 " thick rotors vs 5/8". Would that be "hi vol" enough for you?
This McQuay Norris pump I have appears to be the 7/8 version, got it via eBay and strangely the next town away. As I remember (it's been a couple of months since I got this one) I think he had 2 of them available at the time. Maybe he still has the other? Mine is definitely cast iron and 6 bolt.
You get into HV and you get into higher load on the oil pump drive.... Maybe defeat the purpose of what you are trying to accomplish? Just a thought there.
