I was hoping to get a response to my question. However, I can provide an answer:
Florida will only allow you to expunge/seal your record if it is your first and only offense AND it didn't result in a conviction or if it was an adjudication withheld. I'm quoting from the statute below:
(1) Petition to expunge a criminal history record.__Each petition to a court to expunge a criminal history record is complete only when accompanied by:
(a) A certificate of eligibility for expunction issued by the department pursuant to subsection (2).
(b) The petitioner's sworn statement attesting that the petitioner:
1. Has never, prior to the date on which the petition is filed, been adjudicated guilty of a criminal offense or comparable ordinance violation or adjudicated delinquent for committing a felony or a misdemeanor specified in s. 943.051(3)(b).
2. Has not been adjudicated guilty of, or adjudicated delinquent for committing, any of the acts stemming from the arrest or alleged criminal activity to which the petition pertains.
3. Has never secured a prior sealing or expunction of a criminal history record under this section, former s. 893.14, former s. 901.33, or former s. 943.058, or from any jurisdiction outside the state.
4. Is eligible for such an expunction to the best of his or her knowledge or belief and does not have any other petition to expunge or any petition to seal pending before any court.
The application is available on line. Expungements and sealings can be done without a lawyer. The state website will go over eligibility and will link you to the necessary forms.
If expungement or sealing is not an option, one thing you can do to would be to petition the governor of Florida for a pardon. You can read about it and get the forms to fill out here.
The office of Executive Clemency does the screening for the governor. A full pardon would not erase your crime but would be official proof that the highest official in the state believes you to be rehabilitated. You would not need a lawyer to apply for a pardon. Though they are tough to get, you'd have nothing to lose by giving it a try. They are free to apply for, and, if your record has been clean for 40 years, you'd have a better chance than most to obtain one.
The second possibility is a longshot that would require hiring a lawyer who could petition to reopen your case and try to get the judge to dismiss it in the interest of justice. This would not be supported by the penal and procedural laws of Florida and you could expect the DA and, if available, the victim, to oppose the petition. So the prospects for success are not high.
However, a judge always has power under Equity to grant a petition like that even when the law doesn't provide for it, if it is necessary to prevent an injustice from occurring. So with a particularly compelling argument, if the judge is willing to hear the petition in the first place, it could happen for you.
Courts are sparing in their use of the equity power and many judges will not touch this at all, but it is something you could explore with a local criminal lawyer who would be able to tell you how viable this would beand whether it would be worth the money you'd have to lay out to get it done.