So I installed an aftermarket steering wheel in place of a 3g one I had in and when I install the wheel with the wheels straight the steering wheel is a little off center (tried moving splines) and it was still a little off center is there any way to adjust the steering wheel under the car like you see in a lot of jeeps (rotate a coupler that rotates (seperates) a shaft to turn the steering
wheel) or am I SOL

Not really. You have to make sure the shaft and its clocking device with the arrow is pointing up and thats a straight shaft! If the wheels are out it then means the tracking is out from the central posistiin on the steering shaft.

If you dont have airbags then its not the way to do it. You have to mark 1 point when rotated fully to find center! More time consuming. Over time you will go out anyway and it is strange why it does so much.