check the FE forum here, but I thought I read that the 330 FT used a smaller crank snout and maybe you could use it's timing cover/motor mount to mount a FE in a 61-64 truck. Never tried this but it might be a solution. Then again, finding a 330 FT truck engine could be a booger.

 

As far as the 292 motor mounts set up with the front snout mount and the two on the bellhousing, This set up was used on the F-250 4x4 in 1965/1966. Also the F-350 4x2 in 1965/1966 used the exact same mounting setup for the 352FE. This set up is a two year only and only for these two models. Standard FE engines with CAST IRON timing cover to take the strain of hold up the front of the engine. This is where I would look for motormounts for your 390 to swap in place of the 292.
Warning: the bellhousing for the 4-speed NP-435 is 1"(one inch) longer than the later NP-435. This tranny hung off of the bellhousing with no tailshaft support. So, unless the tranny has the proper input length and bolt pattern, then get the tranny with the bellhousing.



Eric