[dsraven]

oh man, sorry to hear about the pneumonia thing. been there. take care of yourself, then worry about the truck. it won't be going anywhere in the meantime.
I think it may be better for you to start over and level cab to the parallel point with the frame. by jacking the one end of the cab you affect the body line and since that extends back the length of the box and the front sheet metal it could be quite a shim pack at either end in order to get the body line running straight.
-shim cab to get it sitting parallel to the plane that the frame is sitting at. also ensure it is centered with the frame centerline front and rear. plumb bob works great for that or measure from the same point on each side of the cab-over to the frame. see the link for the assembly manual and you can find frame info for a 3100 in section 2 sheet 24. it will show the drop below the main frame top rail for the rad support. thats a handy dimension for you to know if you want to extend the line from your cab mounts "plane" forward so you know how far below that to locate the rad support brackets. also a dimension from the firewall face (front of dash) to that rad mount center point.
-rough in the front sheet metal to ensure your rad support mounts won't be too low for the new frame (not sure what things look like at that end). you could use a saw horse or floor jack etc to get things roughly sitting where they need to be. also do a quick check to ensure the box will be sitting at the correct height on the frame just to ensure it has room to spare instead of having to raise the floor (unless your plan is to raise the floor)
one thing I did when I was mocking up mounts for my envoy swap was to first get the frame sitting on stands and levelled fore to aft and side to side. then I set the floor pan on the frame and bolted it down (envoy frame and floor/firewall swap). that kept the floor sturdy to the frame. then I lowered the cab (without floot and firewall) down over the frame/floor pan. I used threaded rod through brackets welded to the cab (you could easily find a spot to bolt them on) at all 4 corners. the rod extended down to sit on the envoy floor at the front and the frame at the rear but you could do the same by butting the rods against the truck frame. this was so I could use nuts and washers under the cab bracket to fine tune the heights and get things level (digital levels work awesome for this because they don't rely on your eyeball to be viewing from the same angle each time, which can change the outcome, plus they do a decimal point level instead of being close with a bubble level). I attached a couple of pics to show what i mean. I used the envoy floor in case you are wondering what the hee haw with the trans bump. lol. the funny looking washers under the threaded rod are actually from a set of fwd struts I had kicking around and that scenario works great to keep the rod from moving around when you adjust the set up. the rod doesn't actually contact the floor or frame that way. some wooden shims between the cab and frame worked well and didn't bend or scratch any sheet metal.
anyway, when you get better post up a few pics of your scenario. a full side shot would be interesting. till then rest up man. down time will give you time to ponder and maybe check out the assembly manual if that interests you at all. some of the drawings are a little hard to read so I hold ctr and scroll the mouse to zoom in/out on my desktop pc.