Gotta ask, as none of us are there to verify the condition. Tim is correct though, you could lap in some new valves, install good springs and be done. The reason I'm a little skeptical is simply because used heads are just that, used. If in the event the guides are worn out of spec, and valves are equally worn, springs not springing...you get the idea, that's why I brought up that you may not be ahead excepting the cost of surface machining. I've bought many used parts...some in near new shape, others nearly dead...your , mileage may vary.
As far as your 904 being eaten up behind a near stock 360, I will say there's no better time to do a rebuild than when the engine is out.
