Here's my suggestions:
- Pusher fan may be blocking air flow, try removing it
- Higher temp thermostate (you are already trying this)
- Six blade water pump (8 blades may move water to fast through cooling system)
- Try lower heat range on spark plugs
- Engine running to lean, up jets one size
- Bump timing to 33-34 total
Lastly, new temp gauge or one of those infared heat guns aimed at base of thermostate housing will give you an acurrate reading of actual operating temp.