Hi, you can get the original brackets to hold the pipe - but you have to not put the "T" in the slot and just use the bolts to hold the pipe in - it's not very tidy, and not particularly effective.
A 63.5 mm pipe, is thicker wall and from memory the original bracket sits about 20mm off. Also, the 63.5 pipe sits higher in the lower brackets, which adds to the originals not fitting, but does give a bit more clearance on the cam cover (where the OE pipe has a "ding" in it for clearance).