Anything will fit with persistance and a sawzall. Its been a while since ive seen an FE in person, but IIRC they are roughly the same size as a 335 series (351C/M/400) which in themselves only slightly smaller then a 460.
Unless you are going for orginality, and you want a bit more snap then a 302, i would think a 351W would be somewhat eaiser, plus its been done.
If you do want an FE, id go whole hog with a 390. Or install the 390 rotating assembly into your 360.
Im sure steering clearence, as well as radiator/fan clearence would be the biggest obstacles. Next would be the weight of an FE, but a set of 150 springs (minimum) or 250 (what id reccomend) would fix that.
Youll need to make motor mounts, and do some smash bashin on the trans tunnel. A C6 wont fit a factory tunnel on an RBV IIRC. A 4 speed might work, but to my knowledge theres no 5 speeds thatll accept a T case that will mate to an FE, i could be wrong though, or you could run an divorced case.
But to my original point, if your going for original, have at it (i personally think its a cool idea, even though im not a huge FE fan), on 2nd thought, a 400 would be just as much work, and will create massive torque when done right, and still be original...
But a windsor would be the easiest if we are talking in the 350-400CID range.