I've been blindly using Corpscon to convert from NGVD29 to NAVD88. Have any of you kind folks found issues with your outputs?
CorpsCon has a help FAQ for issues surrounding NGVD29 to NAVD88 conversion, and specifically mentions:
Can’t I use CorpsCon to convert survey data from NGVD29 to NAVD88?
That said, depending on the accuracy needed, you may be able to test your results against something like this modeled conversion from NOAA.