[tucsonjwt]

If you take off the bed you risk messing up the holes in the bed or the bolts/nuts if they are rusted.

The way I did it (twice).

Get a couple of concrete blocks and short lengths of 4x4s and 2x4s until you have them stacked snug against the tank. Remove the bolts holding on the strap. Remove a couple of 2x4s from the rear of the tank. Now you can get up there and unfasten the hoses and the electrical connection on the sending unit. There is a ground strap on the frame with a big lock washer type eyelet that needs to be removed also. Remove 2 x4s from the front, then the back, one at a time, until you have the tank resting on the concrete blocks. Slide the blocks out from under the tank and remove the tank from under the truck. Use a flashlight and remove the hoses. Replace the hoses with new ones. It is a good idea to clean off the grounding eyelet, bolt, and frame surface where it mounts.

If you have a Spectra brand sending unit it will likely cause your gas gauge needle to bounce some when the truck is in motion (some say this is not true.)

Replacing the sending unit is easy. Just tap that tab sticking up (counter clockwise, I think) with a flat screwdriver and hammer until it backs off the tank - be gentle - you don't want to snap that tab off.

I think the sending unit will have installation instructions. I bought genuine OEM Delco o rings because they were rounded like a a traditional o ring and seemed to fit the groove better than the one size fits all type o ring supplied with the Spectra sender.

2 BIG CAUTIONS:
1) WEAR SAFETY GOGGLES, NOT SAFETY GLASSES. THE DIRT AND CRUD IN AND AROUND THE TANK WILL FIND ITS WAY INTO YOUR EYES FROM THE OPEN SIDES OF YOUR GLASSES. AT LEAST WEAR SAFETY GLASSES WITH SIDE SHIELDS.
2) YOU WILL GET VERY DIRTY - WEAR COVERALLS OR DISPOSABLE CLOTHING, OR CLOTHES YOU WILL EXPECT TO GIVE A HEAVY DUTY WASH AFTER THIS PROJECT.

This project is not especially difficult, just time consuming and dirty. If you take your time it will be easy - don't expect to rush through it - allow a full day. I always make arrangements for alternate transportation when I work on my truck just in case something goes wrong and the truck is inoperable.

I forget the exact sizes of the replacement hoses - a cheap digital caliper from Harbor Freight is always handy to have around to measure the nipples on the sending unit to get the correct size.

The LMC catalog has a good picture of the tank, straps, and hoses, wires.
I am attaching a pic of my 83 C20 dual tanks.