Pictures are mighty useful things ya know
I recon using all my years of experience (thats 0 then), they are just a simple form of reducer to suit a certain type of manifold size and exhaust size. If you can get away without using them then you will be better off without any restrictions in your exhaust passage (pun intended)... It will allow a little more power similar to porting an engine.
To see if your existing manifold will fit without the clip on stainless parts, line the gasket sets in reverse to how they fit on the cyl head ports, it should match up with your manifold as per your old setup... Otherwise you will need them in place for compatibility.
I would wait for other people to correct me if I am wrong though (highly likely)