I have not had apart a Nippondenso on this particular car, but I believe it is like another one that I converted and resealed. If so, there is a special seal that goes between the top plate and the compressor. If I am correct you will need this special seal. I got mine in an o-ring kit that I bought from acsource which can be located at www.aircondition.com.
As long as you can access the bolts and there is enough room to remove the cover, you should be able to do this with compressor in car.
Use nylog sealant on this seal after cleaning everything thoroughly with a clean lint free cloth, then thoroughly evacuate the system before charging.