I believe the stock exhaust piping is 2 1/4

as for the reverse lights:

1156 Halogen
50w Single Filament Light
Part Number - 20106 Single Pack / 20105 Twin Pack . Ask Scott at MONCHA about these.

The lense you mentioned for the miata fits the VX but it is for the rear side markers on the VX not the front. No options for the front "side" markers aside from clear corners.com or paint them up with night shades transparent tail light paint for a blacked out look.

Hope this helps