If you wish to upgrade your 6 cylinders cars brakes to 8 cylinder type, either drum or disc, you should also upgrade the steering linkage. This involves swapping in a V8 center link, pitman arm, idler arm and bracket, inner and outer tie rod arms, and tie rod adjusters. These are widely available.

 

Are the 1965 I6 spindle to weak to handle a V8 engine?