FYI,
Mark has specifically mentioned that the cone/surround assembly and dustcap are identical, along with the basket. The main hallmark of the system that keeps getting repeated is its overall efficiency. Some things that could help in that regard beyond the relatively large enclosure are a looser suspension and more powerful motor.
I don't know that the stock LAB 15 is anything special, at least not in a sealed box (it's designed for a horn loaded system). You'd probably get better results just sticking with a UXL or Ultimax 18 in a ~4 cf box. A pair of either with a solid amp behind them along with some signal shaping would give a SubM master/slave setup a run for its money.