IMHO,
I would pull the heads and check the bores...can almost guarantee you will find surface rust in the low result cylinders.
I would also check the heads for cracks and or corrosion.
Even if the engine was "running" before purchase, sitting around with the intake and or exhaust valves open on certain cylinders, surface rust is a certainty.
Again, if it was mine, the heads would have been pulled before it even went into the chassis....IMHO....
