I understand the crawling on you back problems, I've been there. I now have a motorcycle lift which helps greatly.
I can tell you that the round disk is not included in my '99 gearbox. It almost looks like someone placed a neodymium magnet inside the outer cover for some reason. In fact, if this disk is magnetic (or, even if it is not magnetic) it could attach itself to the ratchet mechanism and foul the shifting. Is this thing magnetic?
The pawl replacement instructions your are referring to are for the right foot shifter, to get to the pawl on the right shift assembly you would have to remove the ratchet mechanism completely (although there is one flat head screw behind the ratchet assembly holding the inner cover to the inner gearbox case). If you still have the left foot shifter setup, that design does not require the removal of the entire ratchet assembly to get to the pawl. However, you should be able to visually see if either of the figure 8 springs are broken without removing the ratchet assembly.
If not broken, you may want to leave them be, as the removal of the stop plate will require that you readjust the stop plate on reassembly. It is this readjustment that can prove time consuming as you will need to reassemble the entire ratchet assembly and outer cover, then put the bike on the center stand such that the rear wheel is off the ground. Then test the ratchet adjustment by starting the engine and running through the gears.
When I did this testing, I must tell you it was a steep learning curve until I finally figured out how the stop plate adjustment changed the shifting characteristics. It was during this time that I decided to invest in a motorcycle lift which saved me from repeatedly lifting my old bones off the floor, and made the motorcycle repair much more enjoyable.
In answer to your question, in order to replace the inner broken spring, you would need to remove the ratchet stop plate, then make the stop plate adjustments thereafter.