This seems a lot like an idea I had for my '86 C10 pickup. The previous owner did a real hack job on the wiring when he dropped in the current 350, so at some point I'm going to yank it all and build it up proper.
Since I liked the I6 in my ol' trailblazer so much... it beats the power and torque of the truck's current 350, while being considerably lighter and easier on fuel, I was thinking about grabbing one for a few hundred bucks (yeah, I'm familiar with the wiring harness challenges) and dropping it in.
That's a good start, but then it'd leave some room for possible improvement.
It isn't a 4x4, so I don't already have a front drive to play with. Darn, but I like this truck so I've made that bed already... unless maybe another means of driving the front wheels presents itself, maybe hub motors?
I'm not worried about extended running on battery power, just taking up some of the load when accelerating that much mass, so I don't think there'd be much need for a huge amount of juice. I'd still probably go for 120v, though... if it were do-able.
The other option, which I might have mentioned in another thread (my memory sucks sometimes), was a simple version of the hydraulic hybrid concept, with a manually operated lever to take up the acceleration load. Pressure would be restored to the system with every application of the brakes... adjusted so that minor slowing could be accomplished with hydraulic system drag.
Due to its very nature, I don't think it'll ever approach some other vehicles in efficiency, but this would be more for my own education and enjoyment than anything else. Oh... I'd certainly have it equipped for plug-in charging. Might as well get some juice from the grid to start the day.
Then again.... diesel may still be an option...