The OMS map looks to also be in NAD 27. It shows the intersection coordinates as N21 55.766 W159 30.664. The state of Hawaii GIS department has shape files for the TIGER data. Links to the data are available at this site
http://hawaii.gov/dbedt/gis/download.htm. The site has TIGER and USGS road data for the entire state along with County sponsored data for Hawaii County, Kauai County, Maui County and The City and County of Honolulu (Oahu and Lanai).
I have worked with the TIGER data for Kauai in the past and the TIGER data did not distinguish between paved and dirt roads. The Kauai County provided data is GPS derived but the metadata file for Hawaii County says it is rectified to parcel data and is not positionally accurate. the best approach is probalby to use the NAD 83 TIGER data from the site and augment it with County data if it is better. I suppose I should volunteer to convert the data and make it available for an update to ibycus and OMS. I see that there is a SHP to IMG converter. I will need to learn a bit about the process and what extra work is required for routeable maps. I am heading to Seattle on vacation in a few days so I won't be able to get to this for a while.