That tank looks very much like the tank I bought from Automotive Parts Network. Their part number 14404. My tank came with the stuff needed to extend the fuel pickup down and what was needed to modify the fuel gauge sender. I ordered their tank support kit also as the stock tank supports won't work. The tank did not have the 3/4" vent nipple I needed so I had a short pirce of 3/4" tube TIG welded in right next to the filler nipple. I had the vent nipple installed as high as possible on the tank along side of the filler and the initial fill I got 43 gallons into it.
The only big problem with the installation was it is intended for, I believe, '87 and later. If your crossmember behind your rear tank curves forward on both ends where it goes to the frame there is a clearance issue. I had to cut that crossmember out and replace it with a straight one I made out of a piece of channel. If that is what you run into let me know and I can probably get under there and get you a couple of pictures of how I did it.
Jim