Hi Erwin,
Thanks for responding!
I can confirm I have the same files 3660-3664 in all 3 games from GOG (i.e. the boat looks the same in all 3 games). Marco's Assault Boat mod is high resolution. The original bmp files are low resolution with these sizes (3660: 13 KB, 3661: 25 KB, 3662: 7 KB, 3663: 4 KB, 3664: 4 KB).
If your files are bigger then you most likely have the mod ?
KR