Howdy David:
The 250 swap into a '67 Falcon is fairly involved, but not as difficult as a V8. Best bet is to look for a donor vehicle that has the engine/trannys combo that you want and go from there. You will need everything from the fan to the driveshaft and the air cleaner to the oil drain plug. Don't forget the engine/frame mounts.
Know that the 250 engine stands about 2" taller than a 170/200. The 250 engine/frame mounts will help set the engine lower in the chassis. You will also need to set the 250 back as far as possible to give the fan/pully system clearance. The 250 uses 1 3/4" radiator hoses and radiator bungs, so you will have to modify your stock '67 Falcon radiator or adapt to donors.
A much easier swap would be a 200 engine trans. Engines are not much of a problem, but trans mounts changed a bunch over the years and almost always need to be adapted.
There is a bunch of info on this forum and Most from folks who have real experiences with what they suggest to you. Read- listen= and learn. Get educated, then create a plan, then begin.
Welcome to the adventure.
Adios, David