Rear Wheel Arch Position

[davidimurray]

I was wondering if someone could help me out with a dimension. I'm trying to get as much of my chassis welding done as possible before painting. As such I'm trying to work out where to mount my silencer.

I will be using the saturn rear arches, which are 11.5" wide(I think, not got them yet). Would it be possible for someone to measure the distance from the rear face of BR12 to the front edge of the rear arches so I can work out where to put the silencer?

Cheers

Dave