I find myself rebuilding a 26 engine and the valve
The reamers that we offer for the valves have a pilot on the end to align the reamers as they pass through the block. If you have standard valves in there now, you would have to ream to .015 oversize first because of the size of the pilot. You can not run a .030 oversize reamer into a block that currently has standard valves in it. The pilot on the .030 reamer is made to ream a block that has already been bored to .015 over.