How to fix a locked engine in a 1978 ford f250 custom?

It has set about 9 years

If has siezed from setting you might try pouring trans fluid in through the spark plug holes and letting it soak in overnight then try rocking the crank shaft back and fourth. More than likely it will have to be completly rebuilt

Rip it out & drop another in. Other than originality, not worth fixing.

Drop-in a rebuilt short block.