Differential lock on a 730 Case? I have never heard of it and I have been around those tractors since they were new. The only cable under the dash I can think of might be for the radiator shutters. And most of them were disconnected or removed after the cables failed as the owners didn't want to be bothered with them. I like the design on your cab roof.
As far as starting, the most important thing on those tractors was the manifold heater and enough battery power.

As far as starting, the most important thing on those tractors was the manifold heater and enough battery power.
