The problem is the center part has a counter weight so it wouldn't be able to cycle with the JP specific buffer. You can use a normal buffer and spring combo but you wouldn't get the full benefits. The product comes with a buffer + spring though.
Technically Yes, but you won’t get the extended stroke feature that you get by using the shortened buffer and optimized spring that comes with it.
No. This needs the proprietary Surefire H-S buffer to function properly.