M_Boats: mainsheet track

I am plotting installation of a Harken windward sheeting car setup on my 2004 M17, in place of the factory T track and slide. Anybody know what the present track is screwed into, so I will know what to expect when I install the 7/8" CB track? Additionally, the new track is bolted on 3-15/16" centers (obviously 10 centimeters), but I measured my old track at 4" centers. Is the old track metric as well, and my measurement faulty? (My boat is many miles away at the moment, so I can't remeasure). Thanks in advance for any insights and assistance. Tom Jenkins Scintilla