Keep them, and if possible. spot weld then inside the channels of the stock pans, they go a long ways toward stiffening up the pan, always a good thing.
Yea its a good idea to have them, I am doing the same thing using angle iron in the floor channels. It even says to do this in the book by Peter Ezzell "Building your VW based Dune Buggy" published in '69.
Here in Oz they are, among other things, compulsory. Because the registration authorities insist on full roll cages, side intrusion bars, inertia reel seat belts etc. it links the whole together in a strong unit. I would do it regardless as it will strengthen the side rails a significant amount.
