Honestly one of the major reasons the work on my 15 mm Leviathan grinded to a halt was the release of the Knight model from GW, awesome kit, that I of cause need to build at some point. However my major concern was the how would the two work together size wise? Until now I have only seen pictures of the Knight next to other GW models, but yesterday I came across this blog Brückenkopf which had a review of the Leviathan, which is a fine read by it self BTW, the review contained several scale pics I hadn't seen before as well as a link to video showing the Leviathan vs the Knight, I'm gonna show a couple here, and you can follow the link if you want to see a few more.
Though the size difference is way larger than I had feared, I'm still convinced I'll find a way to convert the Leviathan in a way it will fit in next to the Knight. I'm still gonna give it a go - and I'm sure it will be a fitting challenge.