89 CSX GFX, How do I mount these things!

Hey everyone, so it's about time to start putting CSX 394 back together, and I'd like some tips on the GFX. The side skirts are on, so I'm good there, but the bumpers are my problems. On the bumpers I already have the holes from the factory, on the GFX parts, almost all of the tabs are missing!What did you guys do to fix this problem, someone else has had to have experienced this before! Thanks!

I am curious myself about any possible fix.