1955 Aston-Martin DB3S tested by Reg Parnell with a 3-litre engine, later this car became the RRA Special from Geoff Richardson with a different 2.5 litre engine
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Sorry, DavePieman and Shamrock, but this is as near as it gets, and gets mekubb the point. It wasn't the prototype for the DBR4, but a completely separate venture by Reg Parnell, who at the time was a driver and team manager for the Aston Martin sports car team.
He dug up an old Aston project for a single-seater based on a DB3S chassis and engine, and took over the scheme, finishing the car to take to New Zealand for the winter races. It was heavy and underpowered, and did not shine. As you say, the chassis was later used for the second RRA, now fitted with a Jaguar 2.4 XK engine.
