is this for disconnecting fuel lines before remnoval and reconnecting fuel lines after tank install?

if so, it seems that the length of fuel line under fuel tank would be around 12 inches or so for each, the supply and return lines?

Yes.

It is accessed from below after removal of the pan covering the steering assy.

12" of line is more than adequate, but it reduces the risk of kinks.

Good time to switch to metal tunnel lines.

That is the best way to avoid the kink issue. If the rubber trim around the hole is gone you can split a piece of fuel line and place it around the hole so your hands won't get cut / scraped while doing this.

Access hole? Don't need it.

By making the hoses long enough and looping the them carefully, there is no need to access the hoses from below.

I can lift the tank and support it on pieces of wood between the cowl and the trunk center support without disconnecting any hoses.