1)-First Rule of suspension modification: EVERYTHING YOU TOUCH IN THE SUSPENSION AFFECTS WHEEL ALIGNMENT. Expect to play with all aspects of front & rear wheel alignment regularly if you continue to perfect your Pantera.
2)- factory bump-steer spacers (mid-'72-L model onward) are the metric equivalent of 5/16" thick but every 50-yr old Pantera will vary a little in what they really need.
3)- The rack steering rods should be parallel to the ground. Rack body alignment is not critical. Its easiest to adjust the rods for alignment where they attach to the steering arms. This is most easily done by replacing stock tie-rod ends with 1/2-20 SAE thread Heim joints with Ford-taper end studs, in unaltered steering arms. By coincidence, SAE thread Heims will screw onto stock metric thread steering rods with no alteration needed.
4) Stock suspension spring strengths were something like 200 lbs/inch front & 220 lbs rear. You have a semi-race spring setup, not a comfort setup. Springs are available everywhere in 10 pound-inch variations. Select spring lengths to fit your shocks.
5)- Adjustable shocks should be set for lighter damping at the front & heavier at the rear due to about 60% of the Pantera's weight being in back. The shock's bump-rubbers should be blunt-ended in front for 1/2" more travel & conical rubbers in back for less expected travel. .If yours are reversed, swap them.
6)- when using hook-spanners to adjust spring seat height, its easier if you decide what you need as an adjustment and jack up that wheel to take the weight off it. Do NOT oil the threads to make adjustment easier; it attracts dirt and road grime.
7)- Some adjustable seat-shocks have allen setscrews to lock adjustments, so slack them off before you attempt to adjust height or you can tear up the shock threads..
That should keep you busy for awhile, my friend. There are far more things possible to adjust (caster & camber, anyone?) but you have a nice start. Remember, ALL the above will change wheel alignment so the more changes you do at once, the less times you'll need to get a pro realign.