I had my front sight base off and I noticed that the two taper pin holes are almost 1 1/2 inches apart which is exactly how much to long my 16inch barrel is to put on a bayonet.  So I slid the sight base up 1 1/2 inches and installed the front taper pin through the rear hole of the SB.  I took the gas tube off and ran to the range with my new mid lenght single shot.  Windage was real close.  Now I ordered a smith gas block that I am going to try to cut down and instal with just the rear pin (acctualy I think it uses set screws) then I'll set screw the front hole in SB and there ya go.  Semi auto-mid lenght.

I was going to install a Daniel Defense FF tube anyway, now I can just order a midlenght (I think I'll have to cut it down a little) and my project will be done, and for what ever it is worth I'll be able to attach a bayonet to my 16" gun.

I need to get a life.

What'd you do with the old gas port hole?

I'm still useing it.  The smith gas block sits over it and directs gas into the gas tuble.  This is just like a dissipator setup.