My understanding is that if there were no defects in manufacturing, the engine parts usually wear at the same rate. A high mile engine that uses oil and smokes does so because ALL parts are worn. Bolt on fresh heads that seal better and the stressed piston rings are under a greater load and the oil burning actually can increase.
I had a 360,000 mile 305 in a Chevy truck that still ran great and passed CALIFORNIA smog, but 2 exhaust manifold bolts broke off flush to the head causing an annoying leak. I had a pair of 350 heads freshly rebuilt for another project, so I swapped them over since I needed to keep this daily driver operational and smog compliant. The motor actually LOST power with the new heads and the motor spun 3 rod bearings 10,000 miles later. I should have just rebuilt the whole motor instead of replacing the heads, but I only had a weekend to make the changes. Still, 370,000 miles from ANY gas engine is impressive.