I used the SC100 in the L&M Mako housing when it became available. Interesting story there. The SC100 was discontinued before the housing made it to market!
The SC100 offered good performance in its time and the small size travelled well. Like is always the case, the size of the rig is a trade-off. Big cameras and housing handles better underwater but are a burden to travel with. The big screen of the SC100 is nice, but sighting through it requires you tilt your head awkwardly or hold the camera away. If you hold the camera away it is harder to shoot smoothly. That's true of any monitor-back camera. Top mounting is nicer.
I would imagine that the new, small cameras offer better low light performance and longer battery life in addition to features such as high resolution stills. The SC100 has a bigger screen for its size than you'll find elsewhere. If I were you and I really wanted a smaller rig, I'd consider trying to find a used Mako SC100. IT would be cheaper than a custom and would work better.
I don't have mine any longer but I'm friends with the person I sold it to. If you like I can ask if he still has it.
You will get better results with a navigator and TRV-900, though. It has a flip-out mirror for the screen that works well and is still pretty small. The TRV-900 will offer much better performance.