The Open Forum is always a good place to post if you're not sure where your topic should go. This is a SOHC4 forum, after all, so even if your post could technically go in the "SOHC/4 Bikes" forum, it's still going to get plenty of attention in the Open Forum. Posts in the SOHC/4 Bikes forum don't necessarily have to be technical in nature, but they should be specific to sohc4 bikes in general, or to a particular sohc4 bike.
A question about the history of sohc4 bikes would be fine in the SOHC/4 Bikes section. A post venting about a bad selling experience, even if it was a sohc4 you were selling, should go in the open forum because the main subject is the bad experience and not the bike.