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It could be the r510 TP, R540, R540XD, R580 or R580XD. If it had a big head on it, it was probably the R580.
My Neighbour owns a truck business and has a Scania R580 it has a 16 litre engine does 8 miles to the gallon and kicks out 580bhp(horsepower)!
You must be talking about the Taylormade r500 series. They came out around 5 or 6 years ago. There were 3 drivers in this series r510, r540 and r580. The r580 had a 460cc head so it would have been the biggest. Later they brought out the xd series- extra distance, these came in r540xd and r580xd. You should however check these drivers before you buy a new one as they may be illegal now. If they are illegal you would not be able to use them in any competitions, under the 2008 ruling of the R&A and USGA.