Does the 273 crank turn? Starter work? What carb is on it? 2bbl or 4bbl? Valve covers and intake bolted down? 4 speed or automatic? Driveline in place?
If it doesn't have to be rebuilt you might spend some time and effort to make it run to evaluate your next steps. If it's not seized, it may just need some TLC ( carb rebuild, starter, water pump, alternator, points, coil) and a few other things to run it as is.
If it smokes or knocks, plan to rebuild and swap in the six in while gathering parts.
Use the rusted out one for parts as needed.
