After reading these reply's of which I agree with the only thing I can add is be careful what you wish for. I've done those conversions many times and it gets you close. Totally different datums, both vertical and horizontal depending on where you are. The NGS website tool box has lots of good stuff so go there.
Hey, they invented this crappola, so stick with the girl you brought to the dance. Likely you could hang your hat on that more than 3rd or 4th party software.
At the end of the day, you still have to go measure the stuff and put your stamp on it. Sometimes that not only is easier and faster, but you can rely on your own data. Convert after the fact, not before.
Just me but I wouldn't trust the old NAD27 coordinates converted over to NAD83 for use in staking out search coordinates in a swamp. For all I know they were scaled to begin with. If I had one good WGS84 GPS tie to any of the points referenced on the original old NAD27 map, I'd recomputed new positions to search for the rest using my tied position and the geodetic bearing and distances (obtained by inversing the NAD27 values if necessary). The geodetic bearings I'll be getting via GPS should closely (enough) mirror the original bearings if they were geodetic to begin with, they should put me in the right location to find what I'm after. Taking a bunch of old NAD27 values and converting them to NAD83 in no way guarantees they were accurate (if not precise) to begin with. Back to the old adage, garbage in, garbage out.
Cheers and good hunting!
