A Metric Model in Paper Space established in Inches: If you have a drawing drafted in Metric units, but wish to plot in Imperial English units (feet and inches), you can convert the drawing. If the metric drawing units are 1.00 = 1 Meter, you can Scale the drawing by [39.37], (one meter = 39.37 inches), and change the Units to Architectural Units. This makes it more difficult to edit the drawing with metric information, and all dimensions will need a conversion factor. A better solution is to Xreference the metric drawing into a blank drawing. Scale the Xreference by [39.37]. The original drawing keeps metric dimensions. Set the drawing units in the new drawing equal to inches. Units can be Architectural. You can draw Architectural dimensions over the top of the drawing. You can scale the Viewport in metric scale (1:100, 1:50...) or in an Architectural scale (1/96, 1/48...). Your 1 to 1 inch title blocks will work normally.

If the Paper Space and Model Space Units are different, that must be factored into the scaling of the Viewports. If the Paper Space units represent inches, but the Model Space units represent centimeters or meters, an additional conversion factor must be used to reconcile the units when scaling the Viewport window. For example, if the decimal units of the Paper Space are plotted out as inches, but the model is drawn with decimal units representing meters and the Viewport will be scaled at 1 to 100, each Model Space meter must change to 39.37 inches in Paper Space before it is divided by the scale factor of 100. Do it on the chalkboard:

  
 (Model Space Conversion Factor)(Plot Scale Factor)xPaperSpace

If  1.0 Model Space Unit = 1.00 Meter = 39.37 Inch
And  1.0 Paper Space Unit = 1 Inch
Then:
Model Space Conversion Factor: 39.37 Model Space = 1.0 Paper Space.
and:
Plot Scale Factor: 1.0 Plotted Units = 100 Drawing Units

In the above example, you should enter Model Space and ZOOM to [.3937XP]:
(39.37/1)(1/100)xP=
(39.37/100)xP=
.3937xP

This viewport plots out at 1 to 100 when plotted in inches at a one-to-one plot scale in paperspace.

An alternative is to convert Paper Space to metric units. If the title block is drawn in inches, convert it to millimeters by inserting at a scale of 25.40. In the plot dialogue box, change the plot units from Inches to MM. The above equation still applies, but it is much easier to figure. If 1.0 Model Space Unit = 1.00 Meter = 1000 millimeter And 1.0 Paper Space Unit = 1 millimeter

  
Then: Model Space Conversion Factor: 1000 Model Space = 1.0 Paper Space.
and:  Plot Scale Factor: 1.0 Plotted Units = 100 Drawing Units

In this example, you should enter Model Space and ZOOM to [10XP]:
(1000)(1/100)xP=
(1000/100)xP=
10xP

If one unit in Model Space were to equal one Paper Space Unit (1.00 MM) the Model Space Conversion Factor would be eliminated altogether. In that case, ZOOM the Viewport to [1/100XP]. You can add a scale factor of [0.001] to the dimension text entry to force the dimensions to read "1.00" for 1 Meter.