Bing,
There are a couple steps you should have taken when installing the new dash for locating the new studs, you will probubly not forget the next time.
While the old dash pad is off, and before installing the new, you drill small holes through the second layer of the dash metal (there are two layers) using the old stud holes as a guide. After installing the new dash pad, you simply lay on your back side, find the pilot holes, and run a needle up through the upper layer through your pad, and wala! You have the correct location. This is all so easy before you have the dash back in or your windscreen back on.
Since you don't have the pilot holes for location, your best bet is to:
Through careful measuring, get as close to the location from the underside as you can. Using a small hole saw, like a spot weld remover size, take a plug out of the first layer. You should be able to located the hole from there.
CAUTION: There is not much room between the first layer and the second, the closer you get to the windscreen. So a pilot drill can only be enough depth to get you started. Or you will be putting in a new pad.
The holes for the tonneau studs on my dash in my Series V are covered by the dash pad. I would like to install the studs to accommodate my new tonneau cover. Can someone out there look at theirs and provide a measurement that might get me close to where they are. Then I can stick a pin through the pad to get spot on. Thank you.