We need to know what you want to put it in.
The 250 gives more cubes and more low end torque but does not rev as high or as quickly as a 170 or 200.
The log head has problems providing enough air for a performance 200, a 250 is choked even more. The only real answer is the Aussie 250-2v head, Classic Inlines aluminum head or a very highly modified cast iron log with the log milled off.
As said above the 250 also shares the small block Ford V8 bellhousing flange so finding a transmission that will bolt up is fairly easy. May have to mix and match and modify parts for zero balance or use 300 I6 parts to get clutch and torque converters matched up.
The 250 will work in early Mustangs and Falcons but depending on the vehicle you may need to do some changes.
The 250 is taller so there are some hood clearance issues. The block is wider so you may have to use Maverick motor mounts in some instances and slot the bolt holes so the engine sits a little lower.
On some early Falcons I think you have to flip the center link to get clearance.
Length is the same, excluding water pump.
There are no rear sump pans or pickups so you would have to fabricate one. To best of my knowledge only the later Fox body Mustang's, Capri's, Fairmonts, and Zephyr's use the rear sump pans.
There have been a few cases where guys have welded the bottom of a rear sump 200 pan onto a stock 250 upper pan that had the bottom cut off.