1999 Mitsubishi 3000gt, how can you tell if it is DOHC or SOHC, aka SL or base. It is not a VR-4.?

I have been uming it is an SL, but now am not sure based on the 6k redline. I have a picture of the engine which I can show you on request. I am unable to tell, sad I know. Thank you.