You might need side sickle bars on your head if the crop isnt swathed before harvest, or it has not been defoliated. Machine doesnt need much other that the correct screens. Deere has them across the parts counter for quite a bit of money or you can make your own buy the perforated metal and build simple light weight frames. Use the same chaffer, but change the seive and precleaner elements. You better have good rasp bars too, the alfalfa pods are tiny.
What we do is run six filler plates over the front two concave sections,concaves at 0, fan as low as you can go, and sieves down to 1 or 2 on the bottom and 10 on the chaffer and we have had the best results with our sts, we dont change any sieve sections we just run the stanard ones