The name "Long Jon Arbuckle" is a reference to Treasure Island, by Robert Louis Stevenson, where one of the main pirate characters is named Long John Silver.
when they show that odie slurped a page the writing on the page that garfield holds is invisible
Odie's slurping on the seemingly blank diary pages makes the invisible ink visible, but Odie slurps a few pages that already have visible ink on them.
Garfield: (reading Long Jon Arbuckle's diary) 'These maps I knew to be the property of General Washington, but I took them anyway.' Wow, Jon's ancestor stole George Washington's maps.
Jon: (seeing an angry mob and mistaking) A welcoming committee! I wrote and told them I was coming but I didn't expect anything like this.
Garfield: If that's a welcoming committee, I'm Pee-Wee Herman.
Jon: Did you know that some people thought George Washington had wooden teeth?
Garfield: Wooden teeth? Did he have to lacquer after every meal?
Garfield: Two hundred years is a long time to hold a grudge.