Those Ruston Proctor petrol/paraffin locos (start on petrol then switch to paraffin) were close copies of the Deutz mining design that went back to the 1890s, hence the resemblance to the Deutz at Fotty. The RP at GG (memory playing tricks - were there two?) didn't come from North Wales, and is to quite a wide gauge - somewhere around metre?
As for the Rampton Trust... well, it's what it chooses to be and ultimately, he who pays the piper, etc. But as well as buying the Rheidol, in recent years the Trust has (for instance) published the new edition of Bagnalls of Stafford, and given the Narrow Gauge Railway Society info about progress with the Manx carriages. Plus the Trust's nicely restored Kerr Stuart Wren has visited at least one other railway - it's another of their purchases from the Gloddfa Ganol sealed bid auction (the de Winton Kathleen was another), which brings us sort of full circle. An acquaintance who has been shown round the locos in Surrey suggests that we may have reason in future to be grateful to the PRHT; as and when its museum happens in Aberystwyth, perhaps?