I think that they're built for SubC sized cells. I know for a fact that the Hurricane HK417 stocks used SubC packs....couldn't comment for a clone/rebrand stock.
You should be able to measure the diameter of the openings...that'll give you a good guage. Somewhere on google (here on ASC too I think) is a list of the diameters/lengths of different batteries.
**and for a 417 stock...you'll want to get the lengths of wires between the packs just right...too short and they'll tear the packaging...too long and you'll find it tough to close the butt plate, cause it's tight with the 2 cell pack laying flat in the cavity.