Yes, it's been a while, but since I first wanted to start the project, my skills in working with photoetch have vastly improved, and I got a lot more information about plane painting, etc. But a couple of questions:

1) The kit instructions say the "tunnel gun" would be removed. What is that-or did they mean "turret"?

2) Is the "prop boss" the propeller's hub?

3) The plane is depicted as all blue on the exterior while all the wartime planes I've seen were dark on top and light on the bottom. An error, or was the all blue color the practice for planes used for training purposes?

1. The Tunnel gun was the one in the lower rear fuselage just in front of the tail wheel. It was removed post-war to save weight and open up the space for other equipment. The windows were replaced by sheet metal at the same time.

2. The propeller boss is the dome which covers centre of the propeller.

3. Late in the war, all US Navy aircraft had their paint scheme changed to an overall glossy dark sea blue in place of the 3 colour camouflage used before. The glossy paint weathered better, and it was much less expensive to both apply and maintain, because only one colour of paint was needed.

Thanks for the reply. Ironically though, the kit instructions described the idea of removing the tunnel gun, but the instructions show its installation. It does not illustrate how to build the Avenger without the tunnel gun.

They probably want you to just not install the gun. I've trawled up a few pictures which show how the windows were replaced by sheet metal.
http://www.jauntycamera.com/wp-content/uploads/2012/10/30-IMG_7843-Grumman-TBM-3E-Avenger.jpg
http://www.air-and-space.com/20080517%20Chino/BL2_1952%20TBM-3E%20N7835C%20right%20side%20l.jpg
http://4.bp.blogspot.com/-gZD7DRGYHj8/TfugcH6OhzI/AAAAAAAACOY/a8KNmvgEpYQ/s1600/TBM-3R+53587+%2527AZ%2527+HEDRON-1+Korea+1951.jpg
Note that from the side, the former window area was slightly notched back and replaced with a flat panel.
http://4.bp.blogspot.com/-uGi2xjYMymw/TdCR6GBKKMI/AAAAAAAABNA/DJnceYBQmHM/s1600/GrummanM-3R_web.jpg

Many current warbirds have been left with the post war tunnel gun mod intact, such as this one:
http://blog-imgs-18.fc2.com/m/i/l/militaryworld/080210avenger-2.jpg