Tim - I just want to say, this whole thread has been extremely inspiring.
You are worried you have permanent damage, and i understand how difficult it can be to stay positive in a situation like this, but just remember how far you've come... after have a disc replacement! You have added 15# in 8 weeks.. well it's slower than you'd like, but you're making progress! As long as you continue to make progress, regardless of how slow it is, then there is clearly nothing that is permanently holding you back. Think of it from the bigger picture... You will be strength training for YEARS... it's only been a couple months. Maybe your progress won't return you to pre-injury PRs as quickly as some other testimonials you saw.. no two people are the same and no two injuries are the same, but the fact remains that you had a surgery on your spine and you are fighting hard for every inch, making consistent progress toward recovery. a year from now you'll be sitting looking back on all this with a sense of pride at how far you've come. You're doing exactly what you need to be doing, and it's working! It just takes a while, but that's an exercise in discipline and mental fortitude and it will make you a stronger person both physically and mentally.
Just keep at it. You're doing great. Sure, maybe there are better rep schemes you could be doing, or this, or that, but at the end of the day you're doing what you have to do.
Also, you know you're not going to get advice to do any extra volume iso work for the triceps here.. but if you want to do it and think it might help, then just do it. It can't hurt, can it?