I would stick to just building the 4L80-E to handle extra power. If it is built right it will truly hold more power then a 6.5 can make. The NV-4500 really is not geared that great. It has way to much of an RPM drop between 3rd and 4th gear.
I know kennedy sells a DMAX lift pump kit for the 6.5, but also didn't know that heath was offering one. Should be a very good pump for a 6.5. The one down side is I am pretty sure they do not prime themselves.
I change all three of our trucks at 5000 mile intervals. Makes it easy to remember when to change them. I did stretch my 93 6.5 out to 10,000 miles a couple times using the
AMSOIL heavy duty 15W-40. The oil analysis came back fine. My truck actually uses less oil since switching to AMSOIL.
I hope also that it turns out for you. It worries me that it looks like two buyers have backed out of deal. But that is one heck of a deal if turbo is good.
We put in an outside wood boiler that we can heat the house and shop with if we chooses from. Plus heats hot water in house. Will never go back to anything else. Get all the benefits of cheap wood plus don't have to have the wood in house.
It could work cause the first generation DMAX didn't have the VVT turbos did they? You could run them with a simple system like a turbo master right. I might be wrong though.