The handbook is a small document that gives a quick summary of stuff the operator would need to quickly know such as the switch matrix, lamps, coils, fuses, etc. Handy, but it is just the basics. The manual has everything, so it is what you want.
Edit: I believe there is a separate WPC schematics manual that contains all the schematics that aren't in the game's manual. I think TOM is in the era when there was a separate manual.