Well theres a couple of things your going to have to do.
First is find a set of 351-400 m motor towers so you can drop the
460 in. I believe you can relocate your 360 mounts (but dont quote me on that).
Your going to need a c6 trans for a 460 also, take the internals from the 360 c6 and install them in the 460. This should allow you
to keep your currenty drive shaft lengths.
And dont forget about headers for the exhaust.
Now if you go the c6 route for the 390 you'll need the c6 out of
a early to mid 70,s highboy.
I currently have a 76 highboy with the 360, c6 , Np 205 case with dual Dana 60,s
I changed from a divorced tranfer case to a Connected one. I plan on putting a 390 in next year. But my plan is to do a 76 highboy chassis ground up with a 460. The 460 will be stroked , I m looking to get about 570 cubic inches out of it, this should really haul, it will get a Divorced transfer case with the c6 trans. It will also get lower gear ratios in the diffs to allow some low rpm highway cruising but still haul ***. But it all comes down to your budget and what you want to do.
I currently have a 74 F-250 highboy with a 390 bored out to .30 over. It has an RV cam with an edelbrock intake and a holley 770 street avenger carb. I recently had it dynoed and it was making 188 HP with 260 Ft-Lb of torque at the rear wheels. It was estimated that it makes about 250 HP at the flywheel. I plan on installing headers and aluminum heads later on. In my opinion the 390 pulls real hard and with a little tweeking it can become a very impressive engine. The 460 on the other hand has the benefit of more cubic inches. I like the 390 because it bolts right in.
That's tough to decide... I really like my 390, and in your case it would bolt right in, and the accessories would all fit. But knowing 'there's no replacement for displacement' and then reading the past post "wow, what mileage", I'd be leaning toward the 460. But that would involve swapping perches, brackets and exhaust...
The 390 will be direct bolt-in replacement. so that would be easier if you were keeping the tranny. Since you want a C6 instead of manual, you still have a tranny search on your hands. 460 parts are more common since its still a current engine, the FE hasn't been put in a truck since 76. I have no complaints with my 390 other than the oil seepage out of almost every gasket on it. Seems to be a common problem with all FE's. For a total heart/lung transplant, your best bet would be to find a parts truck so you have everything you need for the different engine types. Theres a lot of extras that are overlooked in the planning stages of these swaps (believe me, I went from 300 I-6 4 spd to a 390 with C6). My advice is to find all your parts for each if you can and compare the costs to see if its worth it to you.
What do you expect to do with it? I've got a 460 in mine and you can't beat the torque for out and out hauling power, especially if you're in a hilly area. I haven't had a strong 390 so I can't comment on that.
I'd also say that it depends on what application he is wanting, because yeah, I wou ld probably go with a 460 as well myself, but thats because I just do hauling and all that such. But he doesn't ever make it clear what he is building the truck for. For all we know he wants to make a mud runner out of it, in which case, putting in a 460 wouldn't be necessary at all, and the 390 would work perfectly fine.
So I can better answer the question as can all of you if he would be kind enough to reply, telling us what primary application he is going for.
this is a great thread! i was going to rebuild my 360 to a 390. untill my buddy agreed to sell me the 460 c-6 combo out of his 71 lincoln. the 460 that year in that car is rated at 370HP! after a light rebuild it's going in! here ...hemi, hemi, hemi......
I have seen it done both ways. My brother went from a 390 to 460 in his 76, I went 360 to 390. I personally love the 390 to death. The 460 seems more like a pulling grunt motor. My 390 is more the screaming fun-to-drive motor. As far as pulling power, that has as much to do with gear/tire combo as engine.