If it's a 55 2nd. series, get a bellhousing for the V-8 engine. The 250 is a direct bolt-in for that bellhousing, but you'll have to fabricate side engine mounts for the front. You can make a fake stomp starter by fabricating a bracket and using the pedal to push a starter button that energizes the solenoid on the 250 starter. The exhaust pipe will probably have to be custom-bent also. Labor-intensive, and you'll have less torque than the 235 when you're done, but it's doable. I'd look for a 292 engine, which will require about the same amount of adapting, but it will give you a noticeable power increase.
Jerry
Jerry