NavList:

Sorry Greg

I forgot; in aviation the wind direction is always the compass direction in degrees true that the wind is blowing from.  I.e. a 30kt wind from the north east would be 045/30.  This is opposite to tidal flow tables, which use the direction the tidal stream is flowing towards.  
I quickly drew up a diagram for your figures ( I.e. W/V = 120/30) and got within a degree, a knot, and a minute of you except for your return heading.  If you're drifting left on the way out, you must be drifting right on the way home.  I'll put diagrams up for both W/Vs tomorrow.

An a​​​side, which I'll probly learn to regret mentioning: We do use relative occasionally, but only in one of the various methods of pilot mental DR.  E.g. Max drift is when the wind is at 90degrees to track.  E.g. if TAS is 150kts and wind is 30kts, max drift is 30x60/150 = 12 degrees.  For 120/30W/V, it's at 30 degrees to track.  Sin 30 = 1/2, so the drift must be 6 degrees left, so you need to head 096 degrees to make good a track of 090, or ....... to make good a track of 270.  Max speed effect is 30kts.  Call Cos30 = 0.9.  Speed loss is 30x0.9=27. Groundspeed = 150-27=122Kts or 177kts.   That's how the RAF teach their baby pilots to do it.   Well it's close enough when you've a dozen other things to think about at the same time.  DaveP