I have recently upgraded my Caterham exhaust and replaced the standard 5" side exit stainless steel silencer. It has a matt black slotted heat shield fitted to it.

You can still buy this unit new from Caterham at £270 and can see it here listed as 5" race ford / rover http://www.caterhamparts.co.uk/category.php?id_category=490

It needs a polish and will not meet noise regs on quiet tracks (was ok for Oulton Park at 105db)

£50 ono