Need to fill in gauge area on lift of cluster?

[Envy]

I have a nice rebuilt gauge cluster with factory tach for my 65' chevy, but i want to fill in the left side thats empty. Ive been searching for a while for something i could put there that would look clean and factory.
Considering it has a diesel, id like to somehow incorporate a Boost gauge or Pyrometer. And if i strike out there, something that could monitor the air pressure for my bag system.
Anyone with ideas or references for someone that could build a custom gauge let me know.