Actually, shef, what you wrote is quite helpful.
Since the oscar is staying, it makes perfect sense to keep whichever fish seems to be getting along best with him...thanks for your input!
I've been sitting here watching the convict get chased all over the place by both fish.
Salvini is relentless and forces the convict to stay at the water's surface. Even then he'll still attack him. Whenever the salvini lets up, the oscar is either swooping up under the con and attacking him or doing the 'show-down' move to him (the exact same 'move' he used to do when in confrontations with the previous convict I had to part with). And this whole time the convict is getting more and more tattered...
As a result,
I've decided to keep the salvini and part with the convict.
I moved him to another tank a little while ago, so he should be just fine. Moments ago, when I glanced in on the oscar and salvini, I saw the two side-by-side within about 6 inches of one another---both attacking reflections on the back wall of the tank. It's the first time I've seen them so close to one another without any chasing happening, so that's a good sign. They even seemed to cooperate in their efforts to unite against the convict earlier, so maybe his short-lived presence in the tank will have led to some sort of camaradarie...
Thanks for following along, and thanks to all for the input.
Even though it didn't work out, I'm glad I tried. With the right mix of individuals, I think it's possible, but it just wasn't in the cards for these particular fish. For what it's worth, I wouldn't recommend that anyone attempt this sort of setup unless they've got an immediate backup plan in place. Things can get nasty in a hurry, and the salvini and oscar can pack one heck of a punch.
My 75 gal. tank is now officially 'BV's Oscar & Salvini Tank.'
It'll be interesting to see how these two work out together in the long-run...

opcorn:
BV