nice find drakkol! that is an impressive castle! it just show how versatile these kits are, and very easy to convert!
it should work with 18mm perfectly. This big castle would also work with warhammer! because of the size of the walls it wouldn't show they are smaller and looks like he converted the gate and doors up to 28mm.
the merlons and windows are allready a bit out of proportion compared to the walls and are suited as they are for 28mm
Drakkol, I'm looking forward to what you'll do with it !