It looks like an aluminum frame so that frame is done. Aluminum doesn't do well being re-welded. I haven't heard of Growler and the picture I saw looked like it was modified so who know what was on it stock to make any real comment on it.

I would look at Surly as I doubt they are going anywhere anytime soon and it is a steel frame so can be re-welded as needed be. Just figure out standards and see if the parts match up or just build something new. You can get Surly from your local shop so you can get good support there or pretty much any shop that has a QBP account which is probably most shops. Plus QBP sells a lot of fat bike accessories and parts. They also have Salsa which makes some carbon fat bikes and maybe they still do an aluminum frame.

Bearclaw also looked cool and they do a drop bar fat bike in titanium which is super rad amongst other titanium wide tire goodness.