1990 K-1500 350 chev oil consumption question

I have a 1990 Chev K1500 4x4 with a 350 in it with 138,000 miles. It goes through a quart of oil every 200 miles ( that's a LOT!). It's been that way for a few years now. No oil leaks, no blue smoke except on engine start. It runs quite well, no plug fouling or missing. I figure it is either the valve oil seals, valve guides or both. Has anyone else had experience with this problem? Did you find a solution for it? Does anyone have enough experience with working on a 350 to suggest if the problem is usually the guides, valve oil seals or both? Is it practical to R and R the heads on an engine with 138K on it or is that asking for new problems? Any comments or suggestions much appreciated. Mike H. Seattle.