Peter, it seems pretty clear to me that there were stradale and racing versions of the OTR, with many things being optional (Weber DCOEs instead of Solexes, Girling disk brakes front and rear, luggage carrier instead of rear seats, four or five speed gearboxes, camber compensator). Even the "Uso e Manutenzione" guide has a picture of an engine with a mechanical fuel pump (standard FIAT), refers to the Bendix electric fuel pump and also has a picture of a car with a tower breather fitted where the manual fuel pump usually goes. The engine in the photograph has an exhaust manifold and muffler that looks like an OT setup. I suspect that this was used for the stradale versions and that the firewall was not cut to allow the other exhaust manifold to be fitted. This manifold bent towards the front of the car, towards the fuel tank and required the firewall to be cut. It entered the muffler in two pipes at the front of car end of the muffler. Interestingly, the photos of the engine also show a chronometric (mechanical) tachometer take-off. Has anyone seen an OTR with a chronometric tachometer or do they all use the standard FIAT electronic one? Cheers Graeme