I did use the crush washer for sealing, but I believe it was 5/8 UNF as I was using the FAQ at the time as a source...... to be honest, I have seen a lot of conflicting info on the actual threading of that sender port. I didn't have a proper thread gauge with me at the time to measure and confirm what it actually is. Also, mine was on a '94 with a 3.9 and V-belts and distributor, I belive there was a change when they went to the GEMS igntion.
My oil line fix
My 100k stopped odometer fix
Brace for impact, I'm in a "modifying mood". Massive thread count inbound.