Chrysler Repair: Mitsubishi 3.0 Engine oil consumption, valve stem seals, mitsubishi engines

Question
We have a '97 Voyager that consumes about 1 quart in 700 miles, with a puff of smoke upon startup. Then engine has about 190,000 miles and is otherwise ok. I suspect intake valve guides/seals are worn. I have a set of heads from an earlier rebuild with good guides.
Question: Which is a better way to go, to replace the heads (engine in vehicle), remove engine and then replace, OR, replace the valve stem seals without removing the heads?  I have all the necessary stuff including a spark plug socket epoxied to a quick-release air fitting.

                  Thank You,
                          Jerry

Answer
Hi Jerry,
That is a judgement call. I would lean toward substituting the heads without removing the engine. I have to admit not having experience on working on an engine while installed in the minivan so I can't know about space considerations in working on the rear head. I know it is tempting to just try to do the guides on the existing heads, but I would wonder whether this can be successful when compared to a seal job done with the heads removed. You might ask at one of the Yahoo Autos groups where owners of Mitsubishi engines exchange ideas to see what others have learned. And if you did the head job you could also do the waterpump and timing belt at the same time if needed.
Roland