That sounds pretty typical, but check your battery cables for corrosion. 6V systems need twice the current for starters so I like to use 2/0 or 4/0 battery cables instead of the ususal #4 or #2 12V battery cables you get at the auto parts store. This greatly reduces the voltage drop across the cables.
You may want to do the spark plugs too, when I first got my truck it wouldn't start until I replaced them and then it fired right up.
