Don't forget the exhaust manifolds are center down exit and will cause all kinds of problems with motor mounts if you are trying to use them in a pickup. The heads have 4 exhaust ports and a huge heat cross over that will leak bigtime if you try to use FE exhaust manifolds. The flywheel is larger and heavier and requires the FT bellhousing, which does have mounting ears. I agree with banjopicker in that the holes may not line up on the side of the block with your motor mounts, but that is doable. The clutch is 13 inches instead of 11 in your FE and splines may be an issue. IMHO the 391 is not going to be that big an improvement over your 360. It will have lots of torque but will feel slugish in a pickup. It would be alot easier to install a 391 in a pre 65 truck that had a 292 originally as it has a similar mounting system.I'd stay with the FE if it was me.