The reamer in tool kit F-126740-TL6 requires the use of a reamer stop for this application. Sonnax includes the reamer stop in newer tool kits for this application. However, if you own an older tool kit Sonnax recommends using McMaster-Carr 98381A619 or another of the same dimensions.
Tool Kit for 126740-06K and 126740-24K.
Sonnax F-Tool kits designed to service a specific bore require the VB-FIX, a self-aligning valve body reaming fixture.