Re: What is the current mechanical condition of ..

From what I have heard, both are in fairly good shape having run in the last 5 years, but I personally would think that 463 might be a better candidate for first overhaul. 463 is lighter and easier on the track than the K-36's or K-37's. At least from the standpoint of total teardown overhauls, 463 was overhauled more recently from the frame up and likely has significantly less miles since a major rebuild. The disadvantage is that 463 cannot share parts with the other locos on the property. If something fails mechanically, the engine is off line until the part is repaired or replaced whereas say 492 or 497 share running gear parts with all the other big K's and the parts are interchanged with fair frequency to keep the engines pulling trains.
Now, beyond all that, I would personally rather see 463 in steam than one of the big engines. There is no question that the K-36's and K-37's represent the ultimate in narrow gauge motive power technology. In a way, they are the superpower of the narrow gauge. But, I prefer the smaller motive power from the earlier days of the narrow gauge in Colorado.