Turbo Glide and Superior Turbos both used to sell turbo kits for 637's. They used their own cast manifolds. A friend fitted a Turbo Glide kit about 3 years ago on his crewcab. This involved turning the manifold upside down to fit in the crewcab engine bay..... That allowed the turbo to sit a little further forward. On the single cab you obviously have more room at the rear and the turbo normally sits opposite number 3 cylinder. I've driven plenty of 637s back when they were a current model fitted with Superior Turbos kits..,,... A really really great conversion and was a common upgrade then. Surely they can still provide the cast manifolds at least.