By the time you cut the barrel and re-set the front sight it could be expensive. Unless you have your heart set on 3.5" barrel, I would say to shop shop around for a 65 with a 3" barrel. It may be cheaper.
The 4" M-65 has a square butt. The 3" has a round butt. I have a 3"m-65 and I love the way it carries and shoots. If you want a shorter barrel you would likely be better off getting a 3" barrel and having it installed. Better yet get a new 3" gun so you can have one of each. Oops, that is the hoarder in my head speaking.