Ring gear access plate

I'm putting a new water pump on my 1991 Cefiro (RB20DET) engine.Not enough room to get the harmonic balancer bolt off even with radiator off,will need to take more parts off.Need info on the following option.
Where is the access plate (and description..size,etc.) so I can lock the ring gear to keep the engine from turning over?Also is there any oil to collect on removing the inspection plate?
Help and advice greatly appreciated.

Generally: between engine block /tranny, accessed from below. Oil doesnt come out from here, although leaking crank oil seal might keep area messy...

Make ' 4" more space': Jack engine up one inch, then loosen engine supports, lower engine down.