To answer your questions:

Any tips or techniques on how to do this easily?
Yes, see below. Its not easy. Expect about 2 to 3 hours of your time, more if its your first time. Expect some back and joint aches later. Work outside with lots of ventilation.

Is dropping the tank easier?
Can't comment. Haven't tried that.

If I leave the tank in, should I drain the tank?
See tips below.

Any things I should look for on the replacement unit?
Get one designed for 900 series. The sending unit is spring loaded because the 900 series uses larger fuel tank. If I remember correctly a non-spring loaded unit is for the 700 series. Look for cracks at all fuel hose attachment ports from over-tightening of clamps. You could clamp your hoses a bit further-in or find another replacement. Look for cracked old solder joints. Sometimes the wires are just left a few strands attached. You could re-solder this.

The unit I have has a fuel pump on a metal clip, not attached directly to the plastic unit. Does this actually go into the tank?
Yes. All go in.


Any helpful tips?

1. Drive the car till the low fuel light comes on. Don't underestimate the effect of fuel fumes. Being a robust person I am I still got nausea and headache doing this job!
2. You could start the fuel tank lock ring turning by using a hammer & a block of wood. A flat blade screwdriver works just fine but may chip away some plastic from your lock ring. Do this slowly of course : )
3. Re-solder the sender wires on top of unit
4. Re-solder the fuel pump connectors. They're crimped and wrapped with heat shrink sleeving. New heat sleeving could be obtained from electronic stores
5. Replace the in-tank fuel pump filter sock
6. When uninstalling the old sending unit (after removing the lock ring) turn it counterclockwise then slowly take it out.
7. Use string/wire to "pull-up" the sending tube (extended by spring) to ease installation.
8. When installing insert the unit with the tube at about 4 o'clock position then turn it clockwise (to 6 o'clock pos) to place it in the tank's fuel baffle. Release the string/wire. Install lock ring and fuel pipes.



Re-solder sending unit wires..


Re-solder fuel pump connectors..


Replace filter sock


Re-install using string/wire to "pull-up" sending tube


Regards,
Amarin.