I have a Sig 716 Patrol and I am thinking of getting a 6.5 CM upper for it.   I understand that the Sig 716 has some particular features that not all of .308 AR parts fit.  

Am I correct to think that all DPMS pattern upper would work with the Sig 716 lower?

Does the lower come with a carbine length buffer tube?  

Will the Sig 716 buffer and spring work with the new upper?  If I need to change the buffer and spring, do I seek out DPMS LR308 buffers and springs, then?

Thanks in advance for the answers!