Resources we've found useful in our sorghum syrup adventures:
Mother Earth News' article Sweet Sorghum Revival: How to Grow Your Own Natural Sweetener
1918 USDA Report has descriptions of 4 major kinds of sorghum (amber, orange, sumac and gooseneck). Amber was developed in Indiana in 1853 from a Chinese sample. Orange is of South African origin with larger stalks and heavier seed heads. Sumac (red top) are from Natal (South Africa) is stout with large broad leaves with the smallest seeds. Gooseneck is also African with a curved "gooseneck" stem with later maturity that prevents its use in the North.
There are not so many 'new' sorghum mills being produced for small scale use these days. This mill from Grainmaker is extremely well made and should last us for several generations.