I have a Remington Model 11 with the then standard 28" full choke barrel. I've been offered a 26" improve barrel. I'm ignorant but do these barrels need to be fitted considering the long recoil system? Any Model 11 experts out there?

I have one in 16 ga. Many years ago I bought a NOS barrel for it and it dropped in with no problems at all. I did the same thing with a Belgian Browning A5. I picked up a new Japanese bbl. to use with steel shot and it worked with no fitting required.
C.G.B.

It may drop in but likely you will need to do a bit of fitting to the barrel rails. This is the norm.

I have an 11=49 Mohawk (12 ga.)I bought an extra barrel for that was used, fit perfectly with no adjustment needed.