Obviously it's going to depend on what sort of shape the whole engine is in. You may not find out the whole story until it's opened up. A busted ring could have scored a cylinder wall, and the piston itself could be damaged. You could have a nasty case of crankshaft end-play, tapered bores, etc. But assuming that it's just bad rings, a one-ring rebuild seems like high effort for low gain. You're going to need to take the head off anyway, and you'll need the full gasket set, ridge reamer and a ring compressor, etc. If you don't at least hone the glaze you'll be sorry, so there you will be, with the head off, and all equipped to rering and hone an engine; you might as well go ahead and do it. I don't know what the parts cost these days, but they used to be pretty reasonable. If the engine is basically sound, I'd do all 6 cylinders and all 6 connecting rod bearings. If you open it up and find it's really worn, you're probably better off with a junkyard engine unless you view this as your opportunity to do an engine rebuild for the fun of it, or to do a stroker or something like that.
