84ranger,
It sounds to me that you really dont need to mess with the timing just yet...Set up your HHO generator to get around 1.5 lpm for your V8...simply plug and play at that point because your running just the carb with no computer that adjusts the mixture for you...
If it does sound like the engine wants to be timmed diffrently, try working at the carb mixture before the timing...
The 1.5lpm is just a general rule of thumb..some folks get good performance with just a little...some need a bit more than 1.5
Overall, your mielage should get better and will also likely help extend the life of that old engine (so long as the rings and valve seals are in good shape)....
Keep digging on the boards here, too...there is a ton of info related to your question
Best of luck!
"You don't always have to know ALL the answers, but you do need to know where to find them."