I have a Fortis Switch handguard on my MV. The Fortis and the Ranier Arms are the exact same handguard, just branded differently. It is a VERY nice handguard.
That being said I wouldn't go out and buy one to put on the WK180-C until you have the rifle in your hands and can confirm the dimensions of the gas block.
These handguards are very slim and do not have a large inside diameter. I can see it having issues fitting over the WK180-C gas block.