Well took some measurements today. The front section before it reaches the power switch/LED is 11""x7", Exact same measurements are on the back where the PSU is. Tower is 24" in height and with the base it is 25 1/2" The metals used in the case are very good quality, although not very nicely tapered to avoid cuts. Here's my rough idea on how I'm gonna do this.
First the case cover. I'm gonna cut it into 3 piece as indicated on the red line. This way I can remove panels separarely and add blowholes. I might have to take this to a machine shop to get a perfectly lined up cut along the edge. The top piece will have a blowhole and a round reservoir on it. I can just fill and bleed on top the case. The side panel will be windowed. All of the panels and front bezel will be painted black.
For the front, I will cut the case open to mount either a 2-199 or 2-302 radiator with shrouds on both sides. The plastic front cover will also be cut open to mount a removable mesh + filter. The small drive cage on the bottom see can be moved so I will put the pump in there and move it further back. Another annnoying thing is the AT style power switch. I will have to change it to ATX standards.
The back is easier than I thought. The slot cover + AT keyboard hole can be removed and the motherboard tray has holes for an ATX motherboard
The MB I/O parts will conflict with the keyboard hole so I will cut the section in red off. All I need to manufacturing is a shallow box with the ATX I/O shield at the bottom and put it into the back, on top of the slot covers.
Now the PSU+ exhaust fan will be the easiest. The original PSU was HUGE. I have idea why it is so big and why it was mounted vertically. There is a holder for PSUs so I can just put the new PSU there and cut a hole in the back right above the PSU to put a 120mm fan in.
Positives for this project:
Case is free, although it must have cost a fortune back in the day.
There's couple of them so even if I screw up on one there's a replacement.
Will be very spacious once done, even with WC.
There's a Turbo button, build in LED mhz counter and Key lock.
ATX motherboard mounting holes on tray. No drilling needed.
The bad:
AT power switch
Will have to buy a front function panel with USB+IEEE1394 ports
The Ugly:
I live in Canada so I got to get the modding done in a month or so or it's gonna be too cold to do it outside the house. I don't want metal scraps/dust and what not in the house.