The problem with going to a later model engine for the EFI setup, is the 351M/400 only lasted 77-82 in pickups. Therefore, there is no such thing as an EFI 351M/400.
460's are plenty powerful, and will do almost anything you could ever want/need, aside from passing gas stations. One would bolt to your current trans, but the frame stands are unique for a 460, as are the accessorry brackets. In the end, it could cost more to swap in a used 460, than buying a reman long block or rebuilding your current engine.
Used engines are not that different from a reman, in that you really never know what's inside. That's where building an engine yourself, or with the help of a trusted machine shop, has a major advantage. You always know *exactly* what was done, and what parts were installed.

 

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Used engines are not that different from a reman, in that you really never know what's inside. That's where building an engine yourself, or with the help of a trusted machine shop, has a major advantage. You always know *exactly* what was done, and what parts were installed.[/quote]


Buying a reman engine or long block from a reputable company and you will have a pretty good idea of the components used as well as a warranty whereas a junkyard motor is a crapshoot

 

I had this debate and went 460. The 400 is good if you can get the compression up and finding someone that understands the low oil pressure issue and address it is another. In the end the 460 got the nod for ease of parts procurement and aftermarket support. It will cost more to install a 460.

 

I had heard good things about Jasper, my mechanic actually recommended them. I put a 4.0 6 cyl long block in my 94 ranger and it would take out transmissions by breaking flex plates, eventually figured out the dowel pins were not right and it misaligned the trans. I went through three of their transmissions as they kept replacing them. Finally got them to replace the motor and trans the last time. The second motor I got from them lasted 80000 miles before it sucked a valve, grenaded a piston and punched a hole in a cylinder wall. The transmission I got from them at around 50000 miles stopped shifting to overdrive.

If you think that their 100000 mile 3 year warranty is a good deal read the fine print. After inspecting their returned product all they have to do is say it was not our fault and you have no warranty as we can not see that our product was faulty. Yes I am bitter but for $9000.00 I was hoping to get close to 400000 like I did with the factory motor. My Jasper experience sucked and you cant trust their warranty since the fine print lets them re nig and you get screwed just like I did and I had a reputable mechanic do all the work. If you buy from them you need to pay some one in their network of mechanics for an install if you want their make believe warranty.

 

I've got a 351M in my '79 F-150 from Four Star Engines. I installed it in 1999 and have about 60k on it now. The only problem I've ever had with the engine is that the rear main has leaked for about the last 50k miles. Not bad enough to make me want to tear into it, but enough to irritate me. Other than that, I've been very happy with the performance of my engine. It gets a pretty good workout on the ranch.

My Crew Cab has a Four Star 460 in it. Four Star turns out a nice product. At one time they were the preferred reman for all the NAPA stores around here.

 

a couple years ago my son bought a reman for his 1999 Suburban from Auto Zone. 3 year/ 36,000 mile warranty.
We have not had any problems with it at all.
As stated earlier, the 351m/400 have retarded cams so buy a reman engine and swap out the cam and you are good to go.
If you want efi, which I love on my 5.0 conversion, you have a lot of options these days from the aftermarket. You can bolt on efi to virtually any carbed engine in a matter of hours.