I too am in North America and all maps fit (with 224 MB to spare) on the resident flash. This is using the maps provided in your link. Odd that it would be different. My Peaklife came with 2GB of resident flash- do you have something different?
The issues are not with directory nomenclature, I attempted the rewrite the sys.txt with the directory structure provided to me from the the download, as well as renaming it to Primo as per your instructions. I had no issues with getting Primo to run (I successfully changed the Navipath), it was getting Primo to recognize the maps outside of Primo/Content.
Your instructions were very clear and all steps were very successful. This was my only hangup (that I was easily remedied once I realized that all the maps fit on the resident drive)