Ron, maybe you'd find it easier to just dust off that old intel PC you spoke of earlier.
Provided the [so called] 4 GB card is less than 4096 MiB [it will be under 4000MiB, ~3.9GiB] Windows will allow it to be formatted in FAT16 [it just calls it FAT in the drop-down]. A partition size of more that 2GB is only a problem if used for MS-DOS booting.
Right click the drive>Format>File System>FAT.
All 2 GB cards are factory formatted to FAT16, so you won't need to reformat a newly purchased card. 4 GB to 32 GB are FAT32, 64GB and over are exFAT. All can be reformatted to other FATs using either the built-in Windows tool or other free 3rd party software such as EaseUS. My personal opinion is that RMPrepUSB is best used for the internal flash memory of all Garmin devices and any cards used in them for absolute compatibility with the Garmin OS.
It will be easier for you to use GMAPTool in Windows too, because the win version has a GUI.
If you are at all uncomfortable about proceeding further with this there's no problem. Someone else may volunteer to test maybe. It's firstly going to involve making a RAW copy of your original CF card data on [preferably] another 2 GB card and testing that in the bike before combining the images. We could maybe try with the 4 GB card formatted to FAT but may have to create a 2GB partition on it to mimic a 2GB card. If that copy CF works normally, we'll then use it for combining the original non-NT and small NT images for further testing. All this is very untested and only based on 'pie-in-the-sky' theory but won't directly involve your original card.
Let me know if you're willing to go ahead or not.