Thurston - I personally just regress the heck out of the defensive metrics and use a little bit of judgment on how to adjust a player's WAR based on their defense. Take Alcides Escobar, who is having a really nice season but has a UZR of ~-15, so only an fWAR of 1.0. I view Escobar as a +5 defensive guy per season, despite the oddball UZR number, so my back-of-the-envelope WAR number for him comes out to more like 2.5. It is pretty tough to judge "replacement level", as in reality it probably varies from year to year and era to era, although I have no idea how much. I think that fangraphs estimates "Replacement Level" as something like 20 runs below average over the course of a season, so you could just subtract 20/600 PA's or whatever to compare to an average player. I'm not sure how you would do the offensive metrics without Linear Weights. You could use something like WPA I suppose, but I don't really care for that approach.