[steam for ever]

I agree. Diesel is hardly represented at all when it comes to narrow gauge railways,and are generally only used to fill in for failed steam locos or quieter times of year.
The FR/WHR/WHR.Ltd all have pleanty of large diesels, however, the sight of total diesel operation might deter some visitors. The railway has a huge area of influence owing to its vast size in heritage line terms, and services are being extended as the railway is further improved by phase 5. With the projected new rolling stock, it could be possible that diesel locos will become used more often for the likely high number of stock transfers.