The Eddystone action was manufactured with ears on each side of the rear sight. To to install a scope base some one had to mill them off and to contour the receiver. Without knowing who he was, it is hard to tell how he did the work. However, most of these modifications were done for the Weaver or Redfield bases.
Your best bet is to take the rifle to your local gun store and try several bases to see which one fit. A good gunsmith could help you also.
Cliffprd L. Hughes