Thanks! Knowing how radical I can modify things (just look at my realtime patch), I'm sure it'll screw things up. :-p
I haven't checked for newer versions outside of the OpenTTD repository, so I didn't know there's an alpha available. I'll check it out later but I can't say for sure if I'll begin moditying that one and posting it, but I've found my way around the source pretty well, so I think it won't be too difficult to add and replace what I did so far.
There's quite some work to tweak the original wagons graphics wise and make them look better, especially on diagonal and vertical tracks. They tend to look like one long tube instead of seperate wagons. In particular the small ones.
And since I run my realtime patch with a higher production rate, I want to add more high capacity (some fictional) wagons like the 130t open wagon in the mod I posted, and the 130.000 litre tanker I added recently. There's something about watching a 5200 ton line of 40 wagons being towed by 4 NS 6400s.
What I'd also like to do is figure out how to create an articulated wagon because I saw an articulated container carrier a while ago and the first thought was about creating one in this set.
For fun and experimentation, I already made a short coach version of the IRM III because I like the looks of the IRM (it's even better than the real thing).