Another website below which gives an idea of how 'complex' the RT structure is. While some of the woodwork and the metal frame may be quite simple, there are other load bearing panels which are certainly not the sort of item which can be knocked up out of a sheet of 12 gauge in a couple of hours; as can be seen in the photographs. Elsewhere pictures of the cab framework indicate the level of skill required to replicate accurately. http://blog.rt3316.com/
Having done a quick mental tally of preserved engine failures over the last few years I came up with 14 that I know of. I received a message only a week ago which hinted at there being at least another two.
The fleet vehicle which is 'going soon' has to start and stop ..and be legal. There aren't many fleet engineers around who would sanction major mechanical unit expenditure on something which will still run albeit noisily. I either runs as it is or it goes now.