There is no way to change unbalanced parameters... So i did it..
Your Github repo is outdated, here the patch: https://pastebin.com/iktEcDh2
Added settings for each Locomotive:
1) max_speed
2) braking_force
3) weight
4) max_power (in KW)
For wagons added:
1) inventory_size/capacity
2) weight
Parameter "max_speed" for wagons is calculated as maximum from locomotives.

Hey, this is great and i would like to include it in the base version of the mod if you're ok with that, however im not quite sure how to actually apply said patch. im going to update the github repo with the current mod files now, so atleast thats up to date...

Also, if you're interested, im rather burnt out of Factorio at the moment and will probably not continue developing the mod anyway, so if you want to, i could give you permissions for the repo and mod page so you can take over.