1958 Omega Seamaster Calibre 321 Chronograph Questions

Hello, I am interested in a 1958 first-generation Seamaster three-register chronograph Ref 2907 with calibre 321 movement, alpha hands and the beefy lugs of the early Omega Seamasters. There’s one for sale at the moment on that unmentionable auction site and it looks the same as the one worn and posted some time ago by Bill Sohne. It is all original but lacks the bezel ring on the top of the case. The seller says Omega quoted him 400 to 600 Swiss francs to replace the ring in 1998. My questions are: How difficult and expensive will it be for me to have the ring replaced or remade today? How rare is this model – I have seen very few surface – and what value would you put on it if it was all original in excellent working condition? Thanks for any information you can provide.