Double check the original waypoint unit format.
The Martin's Maps use NAD27 format
Most digital chart plotters use WGS84
The units look identical degrees, minutes, seconds. However, the NAD27 units are calculated by using triangulation from Meades Ranch, Kansas. The WGS84 units are calculated on an ellipsoid grid of the earth from space. Thus, the NAD27 locations can be off by as much as 200 meters compared to WGS84
There are lots of online coordinate conversion calculators
Here's a good link for you Map Datums
online calculator link online GPS converter