I think a "small" phenolic spacer between the LIM and UIM would be beneficial for one reason. Heat barrier.
Also if you incorporated a way to precisely mate to UIM and LIM together it would almost be a "must buy" for every Duratec user.
As for making it a "large" spacer. Hood clearance is already at a premium (I.E. no room) and you also would be lengthening both primary and secondary runner (lower, smaller powerband) if it were not.
