https://www.myminifactory.com/object/3d-print-mav3rick-modular-sci-fi-tank-kit-in-28mm-scale-86406
Here's a sweet little design I found when clicking around completely by chance. It's not free, and the maker has nothing else in the way of
40K kits (he really likes his Raygun Raptors instead!), so it's easily missed! It covers the Whirlwind, the Predator, and so forth. It's so variable (there are other builds not shown in the above picture) that you could use it as a Leman Russ, Basilisk, and any number of other kits too. Not bad for thirty five bucks!