Before swapping motors, check the distributor gear (easy) or the timing gears ( a bit of a pain). If the motor still has the original timing gears it is highly probable the fibre cam gear stripped. Buy a new set of metal gears, have the cam gear pressed on and you are back in business.
As far as swapping in the early 250, you will notice the cylinder head, manifolds and etc are very different. You will as a minimum, need to modify your exhaust and throttle linkage. There may be some other issues depending on if you need to pass smog checks.
Good luck either way you go.
