I Have A 1979 F-100 With A 351m & Plan To Install A 400 In It's Place.
Does It Matter That The 400 Is Out Of A Car Instead Of A Truck?
Will My 351m Headers Bolt Up To The 400 Properly?
Will All My Brackets Work On The 400?
I Saw A F-150 With A 400 Car Engine In It, And Someone Had To Cut The Frame For The Exhaust Manifold To Fit! Was That Because They Used The Car's Manifold?

 

Yep, if they had used the manifold that came off the 351M it would have been no problem. Unless the 400 is out of the earliest of cars, like a 71 model, it will bolt in place.

Before you go to all that trouble, is the engine in good shape? The only differences in these engines is internal. Keep the old engine close by to pull pieces as you need them such as the exhaust manifolds.

Good luck,
Doc

 

Get the proper headers for the year model truck you have and you won't have a problem. Like Diag said, these motors are the same, except for internal. Your exhaust-routing is dependant on the vahicle type, regardless of what motor you have. I took out a 351M from my truck and had it built into a 400 and used ALL the external parts that I had on it before. Just make sure the exhaust is the proper fit for the vehicle AND motor, not just the motor.

 

You should check out Bubba's M-Block site: http://home.earthlink.net/~bubbaf250/parts/parts02.html. 400s used in trucks after '77 had main web reinforcements.