Since I have so many custom models in my OP+ folder, I definetly do not want to uninstall OP+, so here's what I do.
I go to my specs folder and delete the shiplist and fighterlist. I then go to the OP+ folder and highlight and click copy on the backup copies of the OP+ shiplist and fighterlist that is included when you first install it. I then go back to the specs folder and paste them right in there, and within 1 minute, I'm done
Oh, and on a side note, don't forget to occasionally clear out the "weapons damage" text file in the main SFC folder. It just grows and grows and can easily get into the MB's in size. Just open the text file, choose "select all" and then delete.