Finally found myself a 12" Ortofon RMG-309 at not too bad a price and should therefore press ahead with making a plinth for the SP10. I've also found some Panzerholz and Russ Collinson himself has some, so this could be quite easy. What I have to decide is the design. I know that conventional wisdom is to make a plinth with maximum mass, but I wonder about a skeletal plinth type that the Garrards use (like this). Too heavy a plinth might be the reason why some people feel the SP10s can sound too neutral or 'dead'. This website also seems to suggest this and backs it up with measurements.