Re: Ffast running on the Narrow Gauge.

Guy,

This was the first outing of 1211 after the 1987 rebuild for the 125th Railways anniversary held at Ferrymead.

The string of 7 Diesels were to simulate the weight of a train, in this case the trailing weight would be over 600 short tons, only the first appeared running, the rest set up as Dead.(the blue DJ 3rd from the end could not be mu-ed with the other due to incompatible airbrake schedules.).
Diesel locomotives with Dynamic Brakes make a variable tonnage ratio, just like you saw with the Big Boy runs, the Diesel creating a heck of a lot more drag when needed and eased off if need be. A train consist would be difficult to arrange the variable without the addition or putting off additional vehicles along the way.

From the page of Mainline Steam...
"Just one week before the Ferrymead 125 event of October 1988, J1211 was fitted with new streamlining paneling and towed south to Christchurch. The day before its first mainline trip the loco was given a test-run, from Christchurch to Rolleston return, hauling a long line of diesel locomotives. Its first test steaming since overhaul, the loco passed in flying colours and surprised both public and railway enthusiasts alike, who had not expected to see J1211, let alone a streamlined J.