it's a straight roll of the dice.
you can perform the same tests: cranking compression, leak down, scope down the bores, check the plugs, give a visual to the valve train, check the oil. pull the pan and check the bearings.
that would give you a better picture of were it's at, but it wouldn't necessarily tell you if the head gasket it going bad or the timing chain has an *** ton of slop in it. to get there, you'd need a tear down.
so armed with that info, you could decide if it's worth the risk to do the ol' rattle bomb rebuild (gaskets, oil pump, timing chain) and ship it or drop the coin and do a full tilt rebuild.
the cake cuts the same no matter how you approach it. spend a lot and get a sure thing with a warranty or some kind of assurances; spend a little and accept the risk involved.
