Not so much a comprehensive guide, but check the
HP Computer Museum
They have pictures, specs and some manuals online for not only the
HP-3000 series, but earlier HP-1000 and smaller systems and peripherals.
Let me 'second' the recomendation for that site. I'm interested in
larger-than-handehld HPs (everyting from desktop calculators to 2100As),
and that site is a great resource, full of user and service manuals,
schematics, etc for the machines _and peripherals_. Certainly the first
place I look when I want to see what some odd HP computer device was.