wana build me a beast of a motor for my 76 f 250 4x4 4 speed need to tow 20k
what you guys say.
I got a 105 block 360 to play with or I got access to a 428 block need to find the value to offer tho

 

is the 428 a block only or does it have the crank? you better set a budget to help with selections or we'll get you in deep pockets before ya know it!! stroker crank, aluminum heads, high compression pistons, lightweight connecting rods, full roller valvetrain, big ole' ugly roller cam, victor intake, custom EFI setup- fed by a centrifugal blower of course... the list can and does go on... LOL

 

For that, you're going to want a lot of torque. For torque, you want a lot of cubes. You could either build a 410 or a 428. I'd go for the 428 myself if you can get it in a cost-effective manner.

If you really want to spend money and build a monster, 4.25" stroker cranks are available that would take a .030" over 360 block to 445ci, or a .030" over 428 block to 462ci. A standard bore 428 would yield 456ci. That would REALLY make some big time torque for your trailer hauling needs. I think Scouder has built one of these for one of his neighbors; he can fill you in on the details there if you're interested.

The mirror 105 360 block should go to a standard 428 bore of 4.130". You would want to get it sonic checked of course to make sure it would be safe. The cylinder wall thickness is there, you're just looking to make sure core shift isn't too bad.

The general rules for a torque motor for hauling trailers, as I see it:
1. More cubic inches = more torque = better.
2. Keep the compression ratio lower than the "performance" motors we build here. Somewhere between 9.0 and 9.5 sould be about right. You dont want it overheating or pinging on a big hill with the big trailer.
3. Keep the cam on the smaller side. Something like the Crane 343941 would be about right. IMO it would put the torque curve right where it would do the most good when hauling a big trailer on the highway, while lowering the dynamic compression ratio enough to prevent pinging.
4. Head flow is important to making higher end HP and torque, for getting that trailer moving off the stoplight. Dont forget to port your heads!
5. Headers are a must. The stock exhaust manifolds are the worst design ever.
6. Vacuum secondary carburetor. I dont think you'd like a double pumper on a tow vehicle, even with a manual transmission.
7. Airflow velocity is good for torque, so dont go for the big giant intake manifold. A dual plane is a must. Keep the header primary tubes on the small side for better velocity and torque at lower rpms. This also means no huge valves, as they hurt velocity.

I can recommend builds all day long, but I'd like to see what you're thinking first so I dont get carpal tunnel typing exactly the wrong build.