I put a Volquartsen target hammer and sear from Brownells in my MKII in January. The pull wasn't quite as nice as I expected so I swapped parts around and found the lightest and crispest pull was using the stock hammer and the Volquartsen sear. Your results may be different of course.
I believe that at one time Ruger would do the target trigger job on the standard guns for a small fee. That may still be the case, and if so probably your best bet. Call them and ask.