The Ansco field cameras and studio #5's do share the same spring backs with one difference. while the field cameras have a special clip with metal corners on the spring back and NO registering pins. As we know most cameras of this era including Century field and Studio and the #5 Ansco Studio have the registering pins in all or some of the corners.
I did this on my Studio #5 by using a 8x10 Field camera back and adding the pins. I bought a stock rod of brass from the hobby store and cut it to size. Just make sure when you drill your holes to use one size smaller bit. This will insure a tight fit for the pins. Then just tap the pins in and then I sanded the pins ends so they are smooth. That's it. You'll find you only really the pins on the two sides. This is how I did my 8x10 back.
Here are some snaps to better show what I tried to explain. The 1st shot shows a 5x7 field back and the 8x10 back w/ pins added.The second is 5x7 no pin 5x7 with pins (Studio) and the last is the original 5x7 back without brass clip plates and the converted 8x10 back.
Thanks for confirming this.
It also explains why a forum member had what appeared to be an Ansco back, but with the pins, unlike mine with just the brass corners. I've never had one of Ansco's studio cameras, but have had a few field of their cameras.