Everyone, I am going to share a very simple technique with you and you do NOT have to follow these ridiculous instructions (at least on an 80-85 Spider with FI).
Step 1: Drain your entire cooling system. Good idea if you R&R a thermostat, hose, radiator switch, and so on.
Step 2: Connect all of your hoses and replace the drain plug in the radiator.
Step 3: Remove the temperature gauge sensor connector and remove the plug (nut). See picture.

Step 4: Fill your radiator with 50/50 (pre-mix) coolant. They are all the same so it doesn't matter which one, but I use Prestone. Keep filling your radiator (take your time, you don't want to go to fast in this step because you can add un-necessary air bubbles) until the coolant starts to flow out of the Radiator "T". See picture above.
Step 5: Once coolant has started to flow out of the Radiator "T", stop adding coolant, put your radiator cap back on, and put the plug (nut) to the temperature gauge sensor back on. Plug the electrical sensor back in.
Step 6: Fill your overflow bottle about half way. Screw on the cap.
Step 7: Start your car and have a beer, smoke, or big fat fattie. If you don't engage in any of these activities, take your thumb and stick it where the sun don't shine.

Step 8: Have another beer, smoke, big fat fattie, or thumb experience and let the fan cycle two more times.

Step 9: Shake it all about -- you do the hokey pokey and you shake yourself around -- that's what it's all about!!!
Step 10: DONE!

P.S. You can complete this process with the front end raised or level. It does not matter either way.