Am presuming you've got these one yeh?
Yes they do look nasty so i ended up buying the same but blank ones from my local motor factors and bought some FORD RS sticker things from ebay to replicate the original FORD RS you get.
Fricken stickers flew off

but the mudflaps look much better now without that RS logo
oh and to your question yes the universal block things fit behine your arches and no they dont catch