being your starting a 3 cy engine with a ford 4 cyl starter...
the most cranking amps for the money would be a much better way. Your tractor will start on most any battery, so as consumer digest says.. most cca for the cheapest price will do.
however if your starting it in sub zero weather, or letting it sit in a field for 8 months a bigger battery might be justify the additonal expense.
either way, the battery will last about the same amout of time.. so again cheapest battery with the highest cca will do fine. a car battery with high cca at half the price of the 4dlt will probably last as long.