5) Found old 4.2 disks (borrowed from friend), can't find any 4.3 anywhere, so working with it. Build lppsource and spot, but NIM install fails due to "corruption" of spot - missing some libs... stuck here since it looks like the libs the NIM expects in the spot are post 5L... 4.2 just doesn't have them.
Why not install from the 4.2 CD's rather than from a NIM server?
Did you get any diagnostic CD's/floppies with the system. It has been a long time, but as I recall, firmware updates could be done from those as well.
No idea if it is bootable - I expect not - but there is also a .iso download for all IBM firmware - bith system and devices. I recommend you download and use that should you get the system booted.