The Mark 4 is also available from the OEM with the PowerPro headstock at a higher cost. I think they are calling it Mark4P.(?)
When you upgrade to Double-Tilt, the way tubes do not fully seat into the DT Base Arms. I've wondered if this is true of a factory Mark 7 but don't know the answer. When I made a Mark 4 (previously known as a DT Shorty) I cut both Bench and Way Tube lengths to fully seat. IIRC the difference in tube lengths is less than 3/8" where it would be 3/4" on a regular Mark V/5 base. For this reason, the way tube length of the Mark 4 is unknown IMO.