Here's some additional food for thought...
(Components not to scale, location approximate.)
2.4l diesel engine gets connected to 5-speed manual transmission. That will be a little bit of work, as they were never designed for each other.
On the back-end will go a DC, series-wound, forklift motor. It has both a drive-shaft and tailshaft, so it can physically be connected both to the transmission and a shortened drive-shaft (ala EMIS system)
Since it's a manual transmission, I could just put the stick in neutral to leave the diesel disconnected and drive electric only. That also means I would need a reversing contactor and neutral motor timing if I want to back up without the engine. (I would also need to make sure of some way to keep from accidentally making the motor run the diesel BACKWARDS!)
The batteries will most likely have to go in the bed. Since it's a hybrid, the fuel tank and exhaust system are still there under the bed. However, if I don't carry a spare tire, that frees up a bit of space behind the axle for some batteries.
Of course we don't want to forget about aerodynamics either.
That's just a rough drawing, but I think you get the point - trucks have bad aero, so fix it. An aero-cap and rear wheel skirts should help a bit. The truck might also be lowered, and I can experiment with a belly pan as well.
Well, there you have it, my rough idea, more or less.
Ideally, I'd like to run Open Source motor controller, charger, BMS, and maybe instrumention or display.