NGK br8hsa is the cross over. If you can get br9hsa in your area use it. If not you can get them anywhere in Europe/Asia. I order 6 at a time from Jiangwayne as it is what I use in the Z (colder plug). Repair the holes, and seal all of the shroud TIGHT. Zip ties or whatever it takes. SMART guys figured the fan/shroud combo to work. cutting holes eliminates their work. Your description does sound lean so try a NGK br8hs for chops. It fires closer to the head, and reduces piston temp.. That will show the mix better
Ps You can get a HI flow fan almost anywhere for 15 bucks. I Had one but it blew apart in 3 months so I still use the OEM. You saw my thread about melted pistons right?