Options for more than 2:1 on T-136 transfercase

[mann650]

I'm looking for a way to get a lower crawling gear under an M35A3. The best option I have so far is to try and adapt a crawler box like the Magnum Box or Black Box to the existing t-136. I will likely have to do new drive shafts and relocate the mount back a bit. My larger problem is mating the box to the t-136. Does anyone have the bolt hole layout of the input shaft cover (#11 below)?

I think I will likely have to machine and adapter but I am curious to see what the dimensions are.