The 250 will fit under the hood provided you use a set of 69-70 250 mounts.
65-68 mounts will not work, 71-73 mounts dont work either.
No one reproduces the 250 Mustang mounts, some have modified Maverick mounts to work.
I found a set of mint 250 mounts from a Mustang and paid a pretty penny for them.
In the long run, its cheaper to do a SBF swap.
The 250 is wider and taller than a 200, the water pump is longer and results in fan clearance issues.
1965 Mustang Coupe 289/C4
1967 Mustang Coupe 200/C4
2017 Mustang EB Premium