OK, so I current have a carbine with 16" barrel and carbine length gas system.  I have a mil-spec carbine buffer tube with standard spring and heavy buffer.  I want to re-barrel to an 18" barrel with mid-length gas system.  

Should any change be made to the buffer/tube/spring assembly?

I have been pondering possibly using a rifle stock/tube/buffer with this setup.  Would that be possible?

Thanks!

Buffer relates to stock and tube used.....not gas system length.

The difference in "action spring compression distance" between a rifle and carbine is only 0.1" inches.

Nope. Run it. It should work fine.