K here get a flash light and do this with wheels chocked and truck engine OFF
lay on floor looking up above the throttle pedal with light, actuate clutch pedal with your hand, there is a small shaft and pushrod above throttle that is where you look. the plastic bushing could be worn out and they EYE on the rod end worn, or the whole cross shaft from the clutch pedal to that small arm can be worn as well. You want to make sure that the arm/pin and eye are in good condition, as well that the actuation of the pedal shows no sign of wear in that cross shaft.
this is common on these trucks and generally a simple fix.
Look up in the advanced search, Pictutorial and then Tech 101 for title of thread and my user name there are a few threads I've done on this exact problem and will show you with pictures and so forth whats what.
As for the firewall fix ya maybe it's complex but for those who have done it, they will tell you it's night/day for difference.
Also have someone press clutch pedal and you watch in engine compartment at the clutch master cyl and observe if there is any movement if there is that's showing signs of needing that plate and it fixes it right. As for welding up a brace you likely cannot weld up something that would work as well as doing what the plate does and once it's done it's done!
JM2CW
BTW, I'm kinda well versed on that plate and worn cross shafts and pins...fixed every single symptom at one point or another.