A couple of points:
The phrases "dither fish" and "target fish" tend to be used interchangeably, as if they were synonymous, but they are not.
Dither fish ares those whose visibility and activity gives other, more nervous fish reassurance that it is safe to be out and about. A school of cardinal tetras, for example, can act as dither fish for dwarf cichlids that would otherwise spend all their time hiding under rocks, leaves, and plants.
Target fish, on the other hand, are specifically intended to serve as a focus for territoriality-based aggression. They need to be durable and/or fast. It is also preferable that they be non-territorial in nature, or you are just exacerbating the problem that you are trying to correct.
That is why cichlids are never good as target fish for other cichlids. They just tend to create even more battles, with one side or the other being the eventual loser.
Your 65 gallon tank (I'm assuming the standard 65 shape, which is 36" x 18" x 24") really won't have enough room for the traditional types of target fish (i.e. giant danios or silver dollars). The convicts' territory will encompass the entire tank, and since the whole secret to being a long-lived target fish is to move out of the territory of the cichlid in question, the targets will suffer from not being able to run far enough away.
Your pleco already serves as one sort of target fish, however. In that vein, you might consider adding a synodontis catfish to the mix as well. S. ocellifer is pretty easily available, doesn't get too large, and is more active than a pleco. Synodontis cats are also able to take care of themselves, and should be able to survive even in the face of some "attention" from your convicts.
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