Thank you all for your combined wisdom on this matter.

I managed to find a spreadsheet (link to descriptive page of it below) to
calculate what I hope will be all the corrections needed for sunpos to
estimate the location of the Winter Solstice sunrise a few millennia ago at
the location of interest.  These data, combined with the links y'all have
provided to explain the formulas, should be enough to figure out how to
modify the macro.  It will be interesting to see how much the time of day,
perhaps even the day of the year, has changed as well.

http://jqjacobs.net/astro/epoch_2000.html#download

Luckily for me, civil engineers seem to be satisfied with linear
approximations for darn near everything, so the math shouldn't get to be
too involved.

Regardless of my success or failure, I plan to post back here with what I
find.

-David Wagner

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