Hammer or Kingpin are a straight up swap to your Gunner.
Th Xbikes triple trees are different and fork tubes 1" or 2" shorter. Magnum would be 2 inches shorter, other cross bikes are 1" shorter than the Gunner.
Pretty sure of the length. Researched it all last year just got sidetracked. I have a 2013 Judge project that I'm doing the same swap on.
Motorbikerx a member here did the swap on his Vegas. He'll be along directly to share I'm sure.
Now this is an oddball suggestion. Saw a Gunner with an inverted fork, dual discs, twin 6 piston calipers in a small town near here 2 weeks ago. The owner was in a rush to get going and I wasn't on the bike, so he wasn't going to stop and chat, but when I asked him what it was from he said Kawasaki Mean Streak. It looked a neat fitting. I might do some research on this.