'85 305 Smoking Question
 

I recently acquired an '85 Silverado 4x4, 305 with close to 200,000 miles on it. It smokes quite a bit when you first crank after sitting awhile. Question: would it be worth my while to change the valve guide seals to stop the oil burning or is this most likely rings? If so, how hard is it to change the valve guide seals on this motor?
Thanks