The D7C, released in 1955, was naturally aspirated. The D7D appeared in 1959, and the only major differences between the D7C and D7D was the D7D was now turbocharged - and it came with a new design of full pressure lubricated transmission, so the tractor could work on steep slopes without fear of transmission bearings being starved of oil.
The D7C was 128FHP and the D7D was 140FHP. The D7D was only in production for 2 years, before being replaced by the all-new D7E in 1961.
The main problem with the D7D was the final drives were basically identical to the D7 3T, released in 1944, which produced 93FHP.
So, by 1959 Cat were putting 140HP through final drives that were originally designed for 93HP.
As a result, D7D final drives are the main weakness of the tractor. You need to drain a little oil from the final drive cases and check for metal.
I see where the tractor is sporting modern bolt-on sprockets, so she's had some $$'s spent on her sometime.
However, those track shoes are definitely very thin, and have little strength left to resist bending - despite the grousers being rebuilt and being of adequate height.
The RH track adjuster is shot and is going to need repair. The equalizer mainspring is badly sagged and needs resetting. It may even have one or more broken leaves.
You've got some work to do on that tractor before it gets back to good operating order.
I see nowhere that the tractor has had cable control. Cat hydraulics and hydraulic blades were available from 1947, and they started to become a lot more popular in the 1950's as owners and operators realised hydraulics were lower maintenance than cable control - despite the powerful arguments put up by the cable control lobby (largely led by R.G. le Tourneau).
