Sounds like a nice stock truck and worthy of keeping it original. I do understand the desire to upgrade exactly the two things you're discussing though - they are good choices for upgrade. Having said that, a full resto on that truck's brake job will provide more than sufficient braking - but you are correct in disks being a safety upgrade. Keep in mind, that even though they were VERY sufficient in 68, now everyone else can stop much better than a set of drums or even power disks on a 72 D44 axle with disk brakes which have no anti-skid. So that's a plug for keeping a larger safe distance behind others than you do in a more modern car. If you think you'll need better brakes than the drum setup (i.e. do you drive in a lot of traffic or notsomuch - or lots of rain?), then it's worthwhile and I would hang onto the original axle if you can store it. It kind of sucks to feel like you have to hang onto a giant chunk of metal you may never use just because it's original... and if space is tight, that makes it even harder. NP205 is about the best transfer case ever put in these trucks, but it's worth finding who on here has done the swap to know all the hiccups it will incur. Not sure about what possible crossmember issues, if any, etc etc.
Personally, unless you're often in a bunch of traffic or drive in a lot of rain, I'd restore it to stock. No wrong answer though, your thoughts on what to do to this truck are good ideas. I'd struggle with this decision personally - I like to keep em stock, but I like the original stuff (so I bought a 72
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Would love to see some pics of it when you get a chance! And welcome to the forum!