Which OMC controls. A pix would help
What motor was on boat when you bought it, none?
The controls to run a 1985 Johnson 120hp likely wont fit an electric shift 1962 Johnson 40hp, or vice versa.
If the controls are 'modern' there arent any brands of outboards other then Evinrude or Johnson they will work w either as most other OMC based brands are no longer produced.
If they're vintage controls, they might fit Gale, Buccaneer and several other motors that were based on the OMC but branded w a private label for sale at Western Auto or similar stores.
W enough time, money and engineering you might be able to make just about any control work w any motor.
Since you've posted elsewhere that you aren't well equipped or particlarly mechanically inclined, I moved this topic to the Johnson/Evinrude forum. Your controls will work w either brand as long as the motor is the same type as the controls.
And IF the cable ends fit up to the motor. Cables and ends can be replaced if necessary, but vintage cable ends can sometimes be hard to find.
Good luck w your project.