Their spring is nowhere even close to the dimension of an AR-10 operating spring (Armalite part number EA1095). They can order one and compare their parts, if they want to - they'll find out how far off they are. They used to have a member here (Josiah, Jamin's brother), but he hasn't been active in a long time.
Weird - you also asked how heavy their buffer was, and they answered (kinda) with the internal depth of a receiver extension- without giving a measurement. Their receiver extension should be 7 5/8" internal depth, not "kinda" or "close" but exactly - but that's not what they make. Their buffer should be 5.4oz, but it's 3.8oz.
Food for thought, once again, PSA. Soak up the information, and fix your large frame ARs... if you want.