The source code for pak128 is on the SVN
, where it has pretty much always been as far as I know. The Simutrans sources are on another private SVN which is mirrored onto GITHub.
I am not entirely sure where you are trying to go with your balance ideas. A lot of what you are trying to do sounds like trying to fight broken game mechanics rather than fix the game.
For example the reason why people usually do point-to-point lines is because they get paid for Manhattan haulage distance (not realistic) rather than haulage effort taken (realistic). The reason this is required is because there is no financial viability model so factories will pay what ever it takes to get the goods heading in their direction, even if that is an infinite amount of money due to purposely poor line construction and rescheduling.
The main problem with pak128 is that some of the industries make little sense. The most notorious for this are the Construction Wholesaler and Super Market which each require dozens of 12 long trains per month to keep supplied (not possible by road).
At some stage I would like to improve the industry spawning model to be weighted per factory rather than a new chain every city milestone.