It might be easier to just use flaked maize. But if you really want to include the grits, I'd recommend a cereal mash. This is from BYO and explains as well as I could without thinking too hard:
"In a cereal mash you begin by heating a mash of your adjunct and small amount of your 6-row malt to 158–160 °F (70–71 °C) and holding there for about 5 minutes. Then you heat the mixture to a boil, boil for 30 minutes, and return the cereal mash to the main mash. The bulk of your barley malt can be mashed in at 122 °F (50 °C), then heated to 140 °F
(60 °C). When the boiled cereal mash is added to the main mash, the temperature moves into the saccharification range. Cereal mashing requires a nearly constant stirring of the mash. Using flaked maize is much simpler."