One of the "Diesel Diary" books has a lot of info on the Comet.  Just can't put my hands on it right now.
From memory, the Sydney to Newcastle trips done during the coal strikes used a power car at each end, the drivers using bell codes to communicate.
Power cars worked with 1 or 2 empty cars over the Blue Mountains to Chullora and back for major overhauls, the rest of the trains was steam hauled empty.
The power cars had a luggage bay when fitted with the original 2 Harland and Wolff engines, this space was used up when they were repowered with 4 GM engines (plus the 2 aux power engines), so luggage vans were provided.

Found and scanned some photos from that final trip.
http://smg.photobucket.com/user/Gaz170/library/Silver%20City%20Comet%20Final%20Run

I recall riding the Silver City Comet from Broken Hill to Parkes in 1972. What ever its lack of hill climbing power was it certainly was very capable of a good speed on the level track. Timing the mile posts gave a consistent 80 Mph (130Km/h). I commented on this to a staff member on the train and his reply was that if we were running late we could wind up to over 90 Mph (145 Km/h)! Someone once said that The Silver City Comet was the prototype for the XPT.

I believe the Comet was the first Airconditioned Train but seeing it started sometime in the 1930's and the XPT's in the 70's, I think other trains may have contributed knowledge gained over that 40 year gap to culminate in its design too.

Certainly was the first Air conditioned train in NSW, read a copy of the original poster advertising it, with the words   Brings a new standard of comfort for those passengers traveling by rail in far west NSW, or similar wording.

The Comet had 4 GM 6/110 series engines as the main propulsion units driving through Alison lock up torque converters bolted onto the engines, the engines were coupled up to a gearbox in groups of 2, each final drive was driven by 2 engines and forward and reverse was selected in the final drive as there was no clutches the engines had to be shutdown to change direction of travel. There were also 2GM 4/71 series engines that drove 120v DC generators these ran at 1500 rpm and they supplied power for the lighting, AC, Buffet, air compressors gearbox oil pumps and fuel lift pumps.
    There were 4 braking systems on the train, a straight air brake (as used on trucks), a electric pneumatic straight air brake which caused the brakes to apply and release at the same time throughout the entire train, operated on 24volts. A Westinghouse automatic brake which was used in emergency, the deadman worked on this system and the mechanical handbrakes 2 on the power vans and one on each carriage.
up until the 60's there was no Westinghouse brake, if you were to run out of air only brake was the handbrakes. Was told it happened a few times.

Last run Nov 1989 and served the NSW regional/outer regional areas so I never got to see it run in person. Interesting train though. Here is a segment video from a 1987 episode of "A World Around Us" which looks at various railways around Australia. In this particular segment it looks at the Silver City Comet.



https://www.youtube.com/watch?v=dPYxC16KY0I

This is the complete episode (45 mins)



https://www.youtube.com/watch?v=MLjP9Lag7Co


From what people have said about it seems the train was quite the icon. Was it well known overseas like the XPT of today? According the the wikipedia page there are 3 "sets" in preservation - one which was gifted to a railway museum at Broken Hill, understandably so given how important that train was there, Dorrigo has a set and Thirlmere have a set. Interestingly enough in 2008 the team at Thirlmere got the Power Van 104 operational on a test run:-



https://www.youtube.com/watch?v=0PjYkFDsDzA