Having checked the Wikipedia page on the 60 class, it appears that Beyer Peacock insisted that they be paid an amount if any of the unassembled complete locomotives were to be assembled. Normally the builder would supervise the assembly of locomotives at their destination, and would of course be paid for this. I assume Beyer Peacock wanted to be paid a similar amount should any of the locomotives be placed in traffic. I don't imagine that this would be a large amount compared to the cost of the locomotive.Peter,
Another advantage to the NSW Government of taking the last five locomotives as spares would be that they could be paid for out of revenue and not incur a a charge against capital, which would have to be borrowed money.
More interestingly, in the discussion of the identity change of 6042, the Wikipedia page states that in its final days in service, 6042 (which had carried the number 6010 on entering workshops) had the builder's plate from 6039, suggesting the boiler had been delivered as part of 6039.
The NSWRTM book "The 60 Class" by Groves, Wright and Morahan does not directly address the changes of identity of 60 class locomotives, on page 38 there is a photo of a builder's plate, with the number allocated to 6003, but photographed on 6025.
So we know that 6010 and 6042 both carried in sequence the boiler unit from 6039 and that 6025 carried the boiler unit from 6003. Trying to recall the number on the steel replacement plate I saw at Enfield, it seems likely that it was 7457 belonging to 6045, but I can't recall the locomotive number. This plate would seem to be an effort to avoid revealing the identity of boiler unit to observant members of the public while maintaining its identity.
I don't think there can be any doubt that 60 class locomotive cab numbers were routinely changed at overhaul.
I was just skimming through a Byways book #28 in it there is a photo of 6015 with the Heavy Garratt symbols on it, I mentioned the aspect that 15 was converted to Heavy and then seemingly back to light for its Western Sojourn in the 60's before being put back to Heavy type.
This swapping of cab numbers and other aspects could perhaps explain the changes with 6015 the caption says it was on the west, Dubbo or Parkes from mid 63 -67, on return to Sydney it went in for a class 2 repair, very strange at that point of time for a light type to be overhauled, however 6033 arrived at the LES with a burnt boiler, and it says that 6015 received the dual control fittings from 6033, I would suggest that rather than that taking place its possible/probable a swap of cab numbers along with the boiler off 15 was fitted to 6033 instead.
Looking back, two garratts, 6020 & 40 both had the enlarged and modified cylinders to make them heavy types, but were not fitted with the DC set up, both of them have quite a few photo's showing the ++ signage on the tank and bunkers. Yet both on the west were allowed to work the lighter track areas out from Dubbo and Parkes and were included in the fleet of light types which also included the loads they could haul, and not that of the heavy types.