The studs are indeed as you say! 7/16 diameter and 2 and a 1/2 inches long! Looks like you may be onto something here! Do you have pics in your parts book perhaps?
Yes, it could be an Ariel Brooks. But as you may have noticed on HMVF, there are some doubts about the Ariel Lycett. It was definitely used, but I'm not sure about the details...
@ Steve: do you have a genuine Ariel saddle? Any chance of some pictures here?
Don't think I've got an Ariel saddle, Bruce's saddle looks similar to the saddle on Chris's wehrmacht Ariel, same saddle studs about 8 or 9 coil springs, but can't see what the frame type is with the saddle cover on, maybe Chris could take a photo of the saddle frame minus the cover, might help discover if Bruce has the same type of saddle.