KRH, I too would have thought they would have made many, many, many shocks for 81 YZ250s!
What made me lose all confidence in them getting it right was when I called to try to have them set it up correctly, I talked with the son of the guy who started Works Performance and he came across as having zero knowledge on the bike. When I said something about how surprised I was over the shock having gobs of compression and hardly any rebound damping, his response was something like..."We have a customer in Michigan who has the same set up as your shock and he's not had any problems and HE RACES HIS BIKE". Sheesh, I felt like saying "oh, I only ride mine up and down the driveway, that must be why mine doesn't feel right". They had also messed up by mounting the reservoir in such a way that I would have had to mount the reservoir on the swingarm rather than in the stock position...and that was after I specifically told them I'd be mounting it in the stock position. Back in the day, I bought a pair of their high end magnacrosser shock sets for a 1980 CR125 and I sold those to someone else as they were worse than a pair of S&Ws I had on it (yeah, I know that's ancient history and has nothing to do with today).
After retuning the YZ250 shock, I ended up sending my stock shock to Race Tech and for a bit less money than the WP shock, RT anodized the body, rebuilt and revalved it and also did their 2 spring setup on it and it worked great from the get go!
Again though, I know of a lot of folks who've been happy with WP.