the 240/300 is quite a bit larger than the 144/170/200 engines.
i think you will need to do quite a bit of fabrication to fit one in the engine box.
your better bet would be a 200 or 250 six, or a small V8 like a 289 or 302
If it is a 65. those engines will fit in the doghouses no problem. I cannot say about the motor mounts. The crossmember is a tube style in that year. which are shared by all those engines. Just different motor mounts to the block.
Also the rad is bigger for the 240 and 300.