A 2.8 duraspark distributor is from the years when power wasn't as important as emissions compliance, you can probably improve it more by recurving the centrifugal advance. With the engine running, a timing light attached, and the vac hose removed and plugged, slowly raise the rpm's while watching the timing advance. For best performance you want the centrifugal advance all in by around 3000. I'll bet it isn't, my 77 Mustang distributor wasn't all in until 4500 rpm's. The centrifugal advance mechanism is under the breaker plate and you can tune it some without a teardown. There is a rectangular hole in the breaker plate( not really a breaker plate but it's what the stator bolts to) and with the distributor rotated by turning over the engine you can see the tabs that anchor the springs. One spring will be fairly stiff and ride loose on the tab, the other is lighter and should be at least slightly under tension. If you bend the tabs in the direction that loosens the springs it will advance faster, I'd try just the tab with the stiff/loose spring first. Go easy, one tab at a time, a little at a time. You can see the hole in the attached picture.
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