I agree with Tim and Joe. The 250 is stronger than an ox on steriods when modified. A set of 2.5 HSC rods (6") and pistons (1.60" tall) from a Tempo/Topaz, and a nice thick gasket so the pistons don't hit the head, and you'd have a bomb proof rever. One of those 264 cams, a tubing header and a 500 Holley on a post 1978 head from a Granada with enough combustion chamber for a 9:1 compression, a la Mustang Geezer.
And a tough C4 or 4-speed Toploader. Wish I was American....