Need help with the IDI

[HCSTROKER11]

ok i have owned several powerstrokes but never an IDI..there is a guy who wants to trade me his 91 f350 centurion edition. with the banks turbo. it has 189k miles and i drove it today and it runs and drives great. AC still works and everything..i just have some questions..what trans is in these trucks? the OD button is on the dash under the gauges..there is also a HI and LO switch on the actual shifter..i have never seen one before so i have no idea what it is..if i did trade i would be the 3rd owner..the first owner was an old man who hauled his camper and parked it in the garage and after he passed his wife sold it to the owner now..my truck is a lifted 93 f150 with 177k miles..the pics are below..let me know some more about this IDI

[HCSTROKER11]

and what all is in the "centurion" edition