Ohio's expungement laws have recently broadened and the results may be helpful to you. Under the new expungement law if you have only one felony conviction and no more than one unrelated misdemeanor, you can be eligible to apply for an expungement.
Keep in mind, however, that being eligible to apply does not mean that one automatically gets the expungment. Expungements are discretionary. Be aware that the same judge who sentenced you in 1970 may still be the one to review your expungement, and that because of the nature of the crime, you can likely expect the prosecutor to oppose it, as well as the victim if he or she can be contacted.
So, although technically an expungement can be done without a lawyer, you may not want to do this one yourself. There are lawyers who specialize in pardons, expungments and the restoration of rights, and you'd do better to have a lawyer "package you" for expungement purposes and argue the petition.
You can contact the Ohio Bar Association's Lawyer referral unit
to find an expungement lawyer or use a commercial service such as Martindale.com.
If you consult with an attorney and he tells you that an expungement will not likely be in the cards, you can apply to the governor for a pardon. If you've had no further legal difficulty since 1972, you'd be a better than average candidate.
You can read more about the pardon process here.