Googling around, I found
http://www.mapealo.com/Costaricageodigi ... _datun.pdf(in Spanish) that compares various conversion methods for the Ocotepeque datum to WGS84. The best results are obtained with the three parameters supplied by Dörries and Roldan, leading to an average error of 2.81 meters. I understand this is for lat/lon data.
You might try using Auriga's Geodesic Converter for the task. Auriga is freeware, and although it's meant to run on a Palm OS PDA, there's a pre-loaded emulator for Windows available in the Download page of the Auriga website (
http://www.speleo.qc.ca/Auriga - see the "Trying Auriga without a Palm" section).
After selecting one of the caves in the Main form, use the Cave/Details menu (tap the title bar) to edit its parameters. Select the User datum and tap the Datum button to edit its parameters. The Ocotepeque datum is based on the Clarke 1866 ellipsoid, and the XYZ WGS84 conversion parameters proposed by Dörries and Roldan are 213.12, 9.36 and -74.95. Close the Cave Details form, drop down the Options menu and use the Geodesic Converter to convert coordinates using this new User datum. You may select Lambert coordinates as input and see if that works (assuming you already have some sample data.) If it does, I could add this datum to the next Auriga version later this month. If you connect a GPS (Bluetooth or serial) to Auriga, you may get the WGS84 coordinates automatically converted to another datum upon reception. I could add a Connect button right into that Geodesic Converter (like the one available in the Survey Shot form) so as to display converted coordinates in real time (at most every 5 seconds) without being tied to a specific cave. Keep me posted of the results if you go that way.
One word about Lambert coordinates. They are used in the US, but only for scientific use, contrary to France and Belgium, where until recently, topo maps used them (they now switched to UTM.) Magellan GPS receivers support them, although I hear that their latest receivers do a worse job than they used to. Garmin considers Lambert to be limited to professional use and thus does not support them in its consumer products, instead they suggest Trimble receivers for Lambert.
Regards,
--
Luc Le Blanc
http://www.speleo.qc.ca/Auriga