The machinist that prepared my engine uses K-line Bronze Bullet, smooth wall, valve guide liners. The K-line phosphor-bronze thin-wall liners that were used on my 4.3L V6 Chevrolet heads have a maximum bored hole tolerance of 0.372" to 0.3735" I.D. with 0.530" I.D. Viton rubber valve guide seals. The Manley SS valves have 0.343" O.D. stems (not tapered) with .0015" intake and .0025" exhaust valve stem clearnce. My machinist uses the same K-line smooith wall guide liners on Pontiac heads.The name "Bronze Bullet" refers to the nose of the guide liner which is tapered so it will start in the bored guide hole easily.
It takes a experienced machinist with the proper K-line tools to correctly install and size K-line guide liners . It is not a job for a part-timer.