Awesome script man. I was able to create a perfect custom map with only plains and grassland that wraps both ways. I also of course made it with lots of rivers and forests and no oceans which was perfect for me.
The only problem I found is the map size generation. It would seem to me that the width and height numbers used aren't the ones that are used for a normal map. i.e. If I chose continents, normally without this script the mini-map looks fine. However, with your script if I choose to not override the grid sizes, it seems to randomize the width and height so that it looks irregular in the mini-map. It's not a big deal though because I just use 120 width and 80 height numbers instead, and it came out fine.
Regardless of that minor issue, I think this is the best map script around.

Saved me a lot of time going into the WB just to make the map I wanted.