For a small bit... it could be that the stick or tube aren't all the way down. I don't have an 88 to look at so I can't tell you how far off if any that the stick may be. It doesn't sound very far out.
So you are between the marks but on the low side. It probably wouldn't hurt if you added a little but I wouldn't put in more than 1/3 to half a quart. and see where that gets you.
Some over fill won't hurt most engines. (Some engines easily take an extra quart but don't try that at home as they say.) As long as it doesn't start whipping the oil, which an 88 may do more easily due to the balance unit. If it were to whip the oil you'd likely see the oil pressure drop if it's doing it bad.
Being low is allot worse for most engines. Low can make it really easy for an engine to suck air when cornering or braking. (Low Automatic transmission fluid often does the same thing.) Any time you loose pressure is bad.
It doesn't hurt that the stick is off a little. I would probably add oil any time that stick says add it. The stick may have you a little over but as I said a little isn't a big deal. If you aren't comfortable, just add a half quart when it hits the add line.
