Jeebus, you guys talk a lot but don't say much. 19 pages and the truck has never run?
Having plowed through most of this thread, here's the answers:
The mystery electric box on the firewall is an ancient hydro electric trailer brake controller. It was teed into a hydraulic brake line and a small piston inside slid the lever sideways and drag the contactor up & down the resistor coil. Throw it in the weeds, then throw rocks after it.
To put the 2F in the F chassis, use the F engine mounts drilled to M12, or use 75-80 2F mounts. Don't go hacking up the 40 frame to put 60 ears in it... oops, too late.
At the back, same deal. Use a 74-80 4speed bell with FJ40 mounts bolted to the side. Unlike the front, these are dimensionally identical over the years, so the 68 rear ears will bolt to a 78 BH, but have the bracketry for the driver-side slave. 55 is different from 40.
To make the engine bolt-in, dress it as an F. Use the nifty 68 manifold & adapter & 1bbl carb & air cleaner. that keeps the throttle, choke, hand throttle all stock & easy. Use a header if you got it, but be aware that clearancing of the header tubes to intake manifold will be necessary because the 68-69 manifold is very close to the head. A combination of dimpling the header tubes w/ a ballpeen and some diegrinder action on the intake will get it done. To clearance the intake & header for the M12 2F fasteners, bolt the pair to a scrap F head using all bolts (no studs). Run a 3/8, then 7/16 then 1/2" drill bit into the mounting holes, one at a time, removing & replacing fasteners as the drill is moved from hole to hole. Follow with a spotface bit to get all the holes level. Boom, intake/exhaust done, just need to bootyfab an exhaust system.
Use any 74-78 fuel pump so the hardline to carb will connect to pump, and it won't have the later return hose to cap off, and it's got eleventeen little PH#2 screws on it which looks correct.
On the cooling, don't use the giant aircon FJ60 lower rad pipe. Use the 68 pipe and 68-76 lower rad hoses. For an upper hose, the 81- hose to fit the t-stat housing is NLA. Force a 68-78 hose in there and keep your eyes out for a 79-80 upper stat housing, they use a standard 90* rad hose.
Remove temp sender & holder from the 68 engine & thread into 81 engine to work with 68 gage.
To keep ignition simple, use the vac advance 1968 dissy & clamp. If changing to a 2F dissy, be sure to use the thinner 2F clamp so it doesn't hold the dissy up off the block.
That's all I got for now, HTH somebody...