the simple formula for best speed was best l/d speed plus 1/2 the
headwind. Don't recall the second ever being explained though. Just
seemed to fit.

Not a formula but a rule of thumb that's pretty close - judging by a
number of polars I've looked at. The following article is very
simplistic but was written for a student who had trouble grasping the
concept of needing to stay upwind of the field in strong conditions:
http://home.comcast.net/~verhulst/GB.../headwind.html

Tony