I bought a 78 f250 a while back and it has a 400 motor in it. It had not exhaust manifolds so I picked a setup. The match fine to the heads. I had no bolts.
This truck also came with a spare motor. I was told it was a 400 also. It has the 8 bolts on the valve cover it looks like a 400.
So I went to pull off the exhaust to use the bolts and I ran into this.

The exhaust runs totally different a little longer and they dump more straight back than down. I also noticed that the ports are way bigger.

They are more square than round. The exhaust gasket is not big enough , it covers the ports up.
The number I looked up is telling me it a boss 351.
So what do I really have here?

In the picture the top right and left are the ones I have no idea about which are bigger, The bottom right and left are the ones that match up to my 400 out of the truck

 

You can't tell if the engine is a 400 by looking at it. The 351M/400 use the same block, heads, manifolds, etc. The only difference between them are the crank and pistons. Measure the stroke - a 400 will have a 4.00" stroke while the 351M has a 3.50" stroke. You can tell the difference by the crank numbers, too.

I think the exhaust manifolds/engine you have are for a 351C. Take a look at your M Block in the '78. There's a rib in front and to the right (looking head on) of the distributor...about 0.5" wide, 1.0" high and 2.5" long. The 351C block doesn't have that rib. A 351C also has 8 valve cover bolts.

Take a peek at the casting numbers in back of the oil sending unit and on the block by the starter. You can look those numbers up too....maybe give you more info on it.

Not sure about the Boss 351 stuff.......

 

Boss 351 manifolds would have D1ZE casting number prefix for the right & left.

D0AE-9430-B R/manifold casting number is for a car.

D5AE-9431-AB 351M/400 L/manifold casting number: 1975/76 Torino / 1975/78 LTD/Grand Marquis / 1977/79 LTD II & Thunderbird/Cougar / 1977/79 F100/350 / 1978/82 Bronco / 1980/82 F150/350.

D7TE-9430-AB 351M/400 R/manifold casting number: 1977/79 F100/350 / 1978/82 Bronco / 1980/82 F150/350.

 

Ok I took a look by the starter and came up with these numbers,
DOAE-L
65HO
I also just pull the valve cover
OH7 down between the rockers and number 4 stamped just outside of cover seal meaning 4v head, dont know what the OH7 means

 

That #4 stamped on the heads just North of the valve covers means you have a Cleveland, 4v heads. Yup, you're right.

M block heads have an 'M' on the corner....most of them do, anyway.

By the way, Cleveland heads will fit on the M block.

 

0H7 = Assembled July (H) 7, 1970 (0).

 

It sounds like you might have a 400 with 351 Cleveland heads on it, if that is the case then you need adapters on the intake manifold. I am guessing that the manifolds at the top of the picture are for a Cleveland motor which never came installed in a truck from the factory in the USA. The top manifolds look like car manifolds because of the exit angle on passenger side one which most likely will hit the frame if you tried to install them in a truck.

I believe some 351Cs were installed in trucks in Australia. Australia also had a 302 Cleveland and the heads for it are closed chamber design and a desirable one to have for swapping to the 351m or 400 blocks in the US, they are commonly called Aussie heads.

 

Thank you!

 

So would it be better to rebuild this motor and stick headers on or just rebuild the stock 400 that was in the truck?

What you said about they look like passenger style makes sense, The oil pan is front sump not a rear one.

 

Will I finally figured out what you were talking about (that rib). Yes you are correct my 78 has it and the spare motor does not . So Im thinking its a full 351c.

 

So my next question would which one to rebuild for towing? 351c or 400?

 

400 would be better choice for towing. And dont use the 351c heads. They are designed to make power way up in the rpm range. Great for a hot rod,not so much for a truck.

 

Thanks, will just rebuild the 400 then.

 

The 351C and 400 do not interchange. . The 351C has the small block bellhousing pattern and the 400 has the big block 429-460 pattern. If the spare engine you have is indeed a 1970 351c 4V 300HP,it could be worth some money. Do some research and see exactly what you have.

 

I have a 351M without that casting rib you speak of..and it looks like it was cast that way.

Weirdest thing....has a front sump pan so maybe some car engines didn't get that rib?

It has a BB bell pattern and modified heads.