Hello @Jim G.
Interesting question. You can now do 700 SF ADU ( since your lot is over min lot size they changed the code) which I influenced, this is By Right and could take about 3 months at the quickest to get a building permit.
R-M Requires a Site Development Permit (to get your duplex) This is an additional process for Entitlement before you can apply for the building permit. This is usually 120 day process and has additional fees associated with it from planning stand point . HOWEVER you can get a lot more, you could possibly get a triplex, or larger units. (If someone like myself is involved from Design/Partnership Role, we could possibly squeeze out some value from this.)
San Jose has a General Plan, most likely your R-M is now in Neighborhood Residential Designation, so you must prove your density is compatible with existing neighborhood pattern (50% of properties on your block meet or exceed your proposed density)
Let me know if you want to talk off line!
