I think Billy did have a full turbo technics exhaust at one point, I converted his car from a 220 to a 320 and he bought it for that. If not it might be worth a call to Hughes of Beaconsfeild, they were the installers for these kits when they were new and still had a stock of exhausts in their warehouse a few years back.
I would bin the original Merc cat if I were you, a high flow race cat is alot less restrictive.
1988 Mercedes w124 superturbo diesel 508hp 1996 Mercedes s124 e300 diesel wagon 1990 BMW E30 V8 M60 powered! 1999 BMW E46 323ci project car