A little background:
I have a 78 F-150 reg cab long bed with a 351M and C-6 that I want to start restoring and building soon. The truck runs and drives OK and the Cab is solid enough to fix-up. The bed is pretty well shot so I'm thinking I'll probably flatbed it. I plan on rebuilding the motor and tranny while they are out. My brother-in-law had a 78 shortbed with a 400 in it and sold the truck. A friend of his just bought it back and is building it into a mud truck and putting a 460 in it. I may have a chance to buy the 400 cheap. It ran pretty well when my BIL sold it but now it is leaking oil bad and apparently has some issues. I am trying to get it cheap for the crank and Edelbrock 4v intake that was on it. We're pretty sure it had a mild cam in it and he put a timing chain set in it but isn't sure on the advance. It also has headers on it. I can get the carb that was on it from the last guy that had it for 50 bucks. Holley 650cfm.

Questions:

Would it be better to take the performance parts and crank and build my 351M which is bone stock and I know runs well other than a few oil leaks or just rebuild the other 400? I know the 400 has had a rough life but if I do a full rebuild will it matter? What kind of machine work do you recommend I have done? I want to keep a low budget here but want to do it right the first time. Where are the best places to get flattop high CR pistons fairly inexpensive? What other performance upgrades am I missing for a good strong running torquey 400? Not looking for a competition motor here, just weekend screwing around street truck, mild off-roading.

For the time being it will stay on 33's with stock 3.50 gears and I plan on rebuilding the C-6 and adding a HD converter and shift kit. Any other suggestions?

Thanks in advance for any help or opinions. I plan on taking lots of pictures once I get started.

 

One of the main problems with the 400 is compression. You need to deck the engine or buy a aftermarket piston to get compression. If you deck the engine then you will need new pushrods. If your gonna do a adjustable valvetrain your gonna have to get new pushrods anyways. If you want to stay with stock valvetrain you want to keep valve lift under .500 lift. You will probably get into valve bind with stock valvetrain. One thing I've done and kept cheap is buy a cleveland piston, bush the piston pin on connecting rod to fit cleveland piston. the 400 has a bigger piston pin than the cleveland. We ran the dome piston piston and didn't deck the engine left stock. Also ran stock valvetrain with a 268 comp hyd cam. On the pistons make sure you have snaprings on side of piston. because piston pin floats. gonna have to balance the engine which is a good thing to do anyway. this engine was a weekend mudhole truck and ran for yrs. I'm currently doing a 400 ford with cleveland 4v heads with dual plane intake for a 4wd truck. The basics with 400 is get compression up to 9 to 1 or more maybe 10 to 1 on pumpgas and buy aftermarket timing chain of good quality. Do a little port matching on intake/exhaust. Anything you can do to smooth out the ports is a good thing within reason. The turndowns into valves in heads need lots of work to smooth out. If you don't do any of this it will still run well but not as good and a nice ported engine with factory heads. the engine is a air pump, more air you move the better!

 

I would do the 400 rebuild with flat top pistons and an rv cam. Then youd have a fresh motor thated last a long time, for not much money yet still a stump puller.

 

For about 3k in parts and machine work you can have an awesome motor, i just got mine done. I spent about 5k because i had the builder assemble and install everything, including pulling my old motor and installing this one.

Plenty of power!!! 35" tires and 3.50 gears it will chirp the tires shifting 1st to 2nd

 

I would keep the 351M running and rebuild the 400.
Check the 400 block and heads for cracks before you do anything. I went through nine heads to find two good ones.
Turn the crank, recondition the rods, and get flat top pistons. From there up, there are many good choices.