Hi Flying Farmer,
I think we talked by phone last year. There are no STC'd spray gear currently manufactured for the 12ABC line. If you only wanted to spray your own crops, you could probably manufacture your own gear after looking at several examples on the market. No rocket science involved. If you want to go commercial, you'll need to find an aircraft with log books detailing prior spray gear installed (grandfathered). Or get a 12E with STC'd spray gear, (Simplex) or better yet, grandfathered gear (Isolair).
With a 210 Franklin, depending on your weight, you'll be lucky to get 40 gallons off the ground. A little more with the 235. I do 10 gallon per acre work on orchards and only the 12E or Soloy conversion make any sense.