Help on wiring a jazz bass

Hello,

I need some help on a second hand jazz bass I just got. The previous owner didn't warn me that the electronics were not original.
I knew it had Dimarzio J 123 pickups but I was surprise to discover that I didn't have tone/volume bridge/volume neck but instead I have Tone/Blend/Volume.
It's got two 250k for the tone and the only volume dial and a double pot for the blend.
the Volume and Tone work ok to me and the blend works as well although I get a bit more volume with one pickup than with both on. I am baffled to see that only the bridge seems to be connected to the mass and nothing else (!?). edit : ok I just understood the metal plate is used as a mass bridge to the pots.
The Dimarzio Pickups have the black/white soldered together to nothing and the red and green wires seems to be used which appears to be ok.
I bought Vmod pickups and I am worried that I can't just replace the Dimarzio without altering anything else.
Could someone share some light ? I took a picture of it.

thanks

jonathan