By the info you posted it is highly possible that you have found what many of us hunters have sought. If it is indeed a 4DTV IRD, and the rest of the setup is in tact, I would ask if he could hook it up to check it out before closing the deal. It could have died via lightening, power surge, lost the DCII Id, etc.
There are a number of thing that can and should be checked to validate a 4DTV purchase. 4DTV IRDs use a battery to maintain critical info needed for DCII signal reception. If this info has been lost somehow, the receiver is devalued to a now outmoded C band analog receiver as a dishmover/Corotor (polarity) controller and to catch now sparce ITC analog C band broadcasts.
If this is in fact a 4D IRD there is lots of info on the board for how to determine if it is still usable for digital service.
Get the dish regardless. Pole and (ribbon) cable are replaceable. Take care not to "tramatize" it when taking it down. Bends and warps will cause you grief when you do the reinstall/realign. Damaged mesh will affect the reception performance.
Dont dissasemmble any further than is necessary to transport. It is a good idea to take several pics if the mounting assy/adjustment settings from different angles. Also be prepaired to re-invest in some replacement 1/4"-20 hardware, SS if your budget allows. Removing the LNB mount arms, LNB and scaler as an assy would be wise as these can be warped out of alignment with little effort. I find using two pair of Vice-Grips (or equiv) ideal for snapping frozen 1/4-20 hardware if necessary.
DO NOT disturb the adjustments for inclination and declination.
IF tweaking those adjustments is necessary, that can be done on the reinstall much easier set as they are, rather than doing it from scratch.
When you get time, a review of the info from this site will make you familiar with what you will need to know regarding "C Band Installation 101"
Footprints by Dish Size - Adjusting the Polar Mount for Prime Focus Antenna - C/Ku-Band Satellite Systems - Tuning, Tracking, Azimuth, Elevation, Declination Angles, F/D Ratio, Focal Distance, Inclinometer, LNB/Feedhorn Assembly, Actuator Assembly, C
The main page has lots of links to other related info
Global Satellite Chart--Geo-Orbit Quick-Look--Western Hemisphere--C/Ku-Band Footprints/Coverage, Specs (Design/Transponder/Bandwidth/Launch), Programming, Orbit Position/Inclination, Links
Giood luck, welcome to C Band! It is not "plug n play", very little about this hobby is, but IMO the effort is worth the returns.
Feel free to ask all the questions you want, and keep us posted.