Look on the right side of the bike and you'll see a large plug that takes a 3/8' hex key to remove it. Check the transmission oil level with the bike standing straight up. Now, if you bought the bike used, some people change the dipstick to a knurled knob type dipstick so they can get it out with their fingers. It should be on the clutch release cover close to where the clutch cable goes into the transmission.
Check to see if they both have the same diameter axle. Harley went from a 7/8 inch diameter axle to a 1 inch diameter axle sometime around that time period.
The oil drain and the transmission drain plug is on the bottom of the transmission. The oil drain is the one nearest the left front corner of the pan. The transmission is the one nearest the center of the pan.