Hi,
Unless you know about metal structure and strenghts etc, get some pucka made brackets, you are trying to stop nearly a ton of metal, so the metal has to be right... I hear brakes don't work so well when they have nothing holding them into place.
I think your best bet is to look on the classified adds here and the auction sites for the right spacers. TSR are very expensive, but the do know what they are on about, there are other places though, try typing into google and see what happens.
Cheers
kraM