Buy a Silverstone that has a front splitter and you have the limited edition homologation motor for the 1994 BTCC. You can buy the rear spoiler and front splitter aftermarket from the AO shop, but these were only fitted to the skinny 155. The 95 BTCC 155 had a huge Ned spoiler on the back !!!
I've attached piccys of a "proper" Silverstone (Mine !!!! )
I recall Hormann (think thats how its spelt anyway?) done the "proper" kits which gave a similar appearance to the DTM/ITC cars of the 90's.
They are more than likely out of production now anyway and were HUGELY expensive.............bolting thousands of pounds worth of plastic to your 155 is hardly going to give it the 400+ bhp of the real thing of course