So tooth to tooth is bang on 50mm and the front is 58mm.
That's a pain, most of them have a high innner ring measurement relative to the outer face. These may be close. http://www.ebay.co.uk/itm/50mm-Universa ... 43aef9f88e
Might be easiest to drill the burger off the original ones, sand them down and go from there after all.