and be aware i was talking about the headtube length not the steerer tube length!!!!!!!
Nup, The headtube length can vary, depends on the frames geometry.
I would assume that the seller has left some clearance, to accommodate the varying head tube sizes. Because this runs a direct mount, the steerer dosen't need to be much longer then the head tube at all, just enough for the crown and headset to fit on.
Check with the seller first for the exact steerer length, then measure the distance from the bottom of your steerer to where the top of the top crown is and see if it will fit.
Hope that helped.