An interesting project, but do-it-yourself hybrids are difficult due to the complexities of effectively controlling and managing two power sources.So as much as I love the concept of an EV conversion the 460 in my truck is a beast motor that runs absolutely perfect. I like the idea of creating a hybrid of sorts.
That could actually work, especially if you don't drive the front wheels except when needed for traction or when making use of energy stored in the battery, and if you take full advantage of the front drive motor(s) for regenerative braking. this configuration is essentially what the transverse-engine Toyota AWD hybrids (Highlander, RAV4, etc) do... but their electric-only axle is the rear. Unfortunately, to be worthwhile you need a motor-generator for the rear (not just the front).Currently the truck is rwd. Considering making it 4wd by adding an electric drive system to the front.
You could use a normal drive axle from a 4WD truck, and place the electric motor where the transfer case is normally located. It looks like the 4WD 1990 F-250 (non-HD) used Twin Traction Beam front suspension, and presumably the 2WD used Twin I-Beam. That means they're basically the same design, so the 4WD components may fit into the 2WD truck; however, the 4WD may need to sit higher so that the frame clears the axle shafts and the engine clears the final drive (differential). Even without electric conversion, 2WD to 4WD conversions are not trivial.
That's a series hybrid. They have a big efficiency problem, because the power transmission efficiency of a generator plus motor is much lower than the power transmission efficiency of a mechanical transmission. It can be done, but it won't be worthwhile.The other idea that would require much more engineering is to put an electric drive system in the rear and keep the 460 to power a generator instead of a transmission.