Sorry, but its not as easy as you are probably thinking.
The truck rearend will be too wide and the wrong bolt pattern. Try looking for a 55-64 car or 68-newer Nova or Camaro (double check on width before $$$). The 55-57 will be a "bolt-in" the others will need to have the mounting changed.
If your truck has a 3spd, then hooking it up to the original shifter mechanism on the column shouldn't be a problem, some fab work will be required though.
The 250 is longer than a 216 so there may be issues with radiator clearances. Also motor mounts will need to be made. Not sure, but somebody may make a kit to put one of this in this chassis, try Chassis Engineering or Buffalo??? Throttle linkage, firewall braces, exhaust, etc... will be issues. The "K" member under the car may need to be modified. Driveshaft will need to be made, emergency brake cables, etc....
You will want to convert it over to 12 volts also. Hooking up the clutch fork to the original pedal assembly will probably need to be modified also, the '51 comes out at an angle, the '74 would come straight out the side.
