Better servos and a radio that will allow you to adjust endpoints is a better strategy. OK, as for the DS821's you already have, you can certainly use one each on ailerons. You could still use some Hitec servo for elevator / rudder to save money and just skip the programmer part. You lose some accuracy, but they're OK if you don't mind that.

I don't know what 120 sized hybrid you are putting together, but let's assume it's something close to a full size 2M ship. You definitely do want to get into the 90 to 100 oz-in range for elevator and 120 oz-in or more for rudder. Keep in mind that JR servos are quite happy running at up to about 6.5V, so if you use a good regulator and a 2 cell LiPo pack, you can get that type of output and get more speed and power out of your servos. Since the DS821 is rated at 88 oz-in at 6V, you could get it in to the 90 oz-in range at 6.2 to 6.5V, depending on how you set up a regulator for it. So now you just need to go find yourself an affordable rudder servo.

Go to tech-aero.net and look at my regulators. If you like what you see there, email me using me the support email link and we'll get down to business on how to set up a good system to get your existing servos humming along better, and maybe I can help you out with a used DS8411SA at a good price too.