I just found another site with a motherload of info:
Roman Forum.
It pretty much links to everything I have listed above and then some. Very comprehensive and broken down by building. It's definitely going into my bookmarks.
Just for kicks, I've been playing around a couple of the Brueggerman models and Sketchup with some decent results. Maybe this can partially help you with your architectual and dimenstional problems. This is what I suggest:
1) Use top down view.
2) Draw a line of 10m or 10 yds or whatever units you want to use (just stay consistent).
3) Import the image of the Temple of Saturn (or other simple rectangular building that has a scale legend) into Sketchup along the horizontal axis.
4) Adjust the size of the image using the scale and moves tools until 10 meters on the Brueggerman image is the same as the 10m line you drew.
4) Delete the 10m line
4) Draw a rectangle covering the entire external perimeter of the temple.
5. Delete the image of the temple
4) Import the image of Brueggerman's lower forum into Sketchup as a .jpg (flat along the horizontal axis).
5) Keep scaling and moving the lower forum image until the outline of the Temple of Saturn on the lower forum image matches the rectangle you drew representing the outline of the temple.
6) The lower forum image should now be fairly accurately to scale (without surveying it yourself) and you can construct the buildings on top of the outlines to keep them within the proper dimensions as well.
Even if you cannot find detailed facades with dimensions it should be much easier to reconstruct them with this overal outline scale in sync.
Good luck again!
-Severus