I am putting a 3.5" lift kit in my 2017 Scamp. The axle is bolted in BUT there is a welded strap in the center. What is it for?? I can't see it doing much more than preventing floor bounce when you walk on it. I'll weld in a short extension but it will not add anything to the suspension.
You are correct it's just to support the floor. You are on track just weld or bolt in an extension.
Eddie
I'll do a full report of the project when I get time. The easy answer to putting 14" tires on a 16' Scamp is that it can't be done (with out modifications). I'll show people how I did it.