Stupid rear end questions...

Guys, I wanted to check what was going on with oil and wear my 7.25 rear end. It has some kinda massive torx plug. I have a manual, but it doesn’t say anything about the size or type of tool I need...
another question is I noticed that my speed is higher than what is on speedometer (those digital speeding displays on the side of the roads) if I go around 30, actual speed is around 35mph or so. So what I did I counted tire vs driveshaft revolutions and I believe I have 2.76 gears. I have ‘64 dart GT 225 4speed , in my manual says gears were 3.55 standard and 3.23 optional. So does that mean gears were swapped at some point? Where I could get plastic gears for transmission to fix speedo error?

thank you very much!