With your combo, just about anything will work. The 3.91 gear and 727 3 speed are doing all the heavy lifting, and the cam is small enough that it really isn't giving much away at the bottom end.

So any of the tons of 11" HS types, typically in the 24-2800, or 28-3200 varieties would work. These typically come in the 200-400$ range.

You driving style, and performance goals also play into the decision. If you are married to the 3.91 gears, You can get away with a 10" or 9 1/2", and up the stall into the mid 3K range, but should you decide to throw in a set of 2.76's or 3.23's for a road trip, you may find the looser converter to be inefficient at least, or a heat building pig at worst!

Just a general tip here, but for Dual purpose cars, converters that are "Tight" for their size tend to work best. For instance a 10" 4500 stall is considered loose, while an 8" 4500 is considered tight.