HERE IS A THOUGHT - GIVE IT A TRY:::
Set units to the right spec - inches, ft, mm etc (PROPERTIES etc -- thats the icon 3 or 4 over from left on the first icon bar..)
1 Select (the active) viewport (The one you will import to...)
2. Select Dimension (Linear) from top toolbar - draw a dimension that is close to you want in the direction you are concerned...
3. From (Main/TOP) toolbar--Pull down Scale - pick 2D - work the size
4. Size 'til you get it right?
I've worked some that are 10,000x off (mind you these were *.dxf files, using this way - sorry its crude, but I'm self taught - I think it should work for dwg too -- I'd think.)
Just a thought - give it a try
Hope that helps!