It would be much simpler to use a rebuilt '54 or later 235 or 261.
There are many things in the way of mating a 250 to a torque tube setup.
The biggest issue is how the clutch and brake pedals pivot on the 40 bellhousing. A 250 engine will not bolt up to a 40 bellhousing.
A 235 or 261 will bolt up to a 40 bellhousing.
A 250 is a fine engine, but you would have to ditch the 40 transmission and torque tube rear end. Then you would need to come up with custom crossmembers to support the 250 since it uses side mounts instead of front mounts and bellhousing mounts. Then you would need a more modern open rear axle and a drive shaft, and a more modern open drive transmission.
