I see the logic from both sides of the argument. Either way, just use the vehicle and enjoy it.
I am building my Santana/Defender 110 at a shop that is doing frame off restorations of Defenders. Unfortunately, the 100k+ price tag is actually justified. New frame, doors, top, tub, every nut, bolt, wire, everything. It is a completely new vehicle and takes labor to disassemble and rebuild. I am good friends with the owner and am working on my vehicle as much as I can but need his expertise for 'rover-quirks', welding, suspension and more. He can direct me on next steps and it is slowly coming together but of course taking 10 times longer than expected...
Another argument for using a professional is time...it might take you three months to rebuild that transfer case when u could takr it to an expert for a few days.
I have done a lot of wrenching in my day, but the older I get, the less time I have. Would rather spend the time on the trail than in the garage under the rig.