Chris, re. the rear sight, in this case you might be better off getting a Gamo-type cheapie diopter, which is modelled on the genuine FWB unit. I think they sell for £20 or so. If you can get an FWB sight for under £40 then great, but it might be a big ask. Egun is probably your best bet for a cheap original FWB diopter. Is the stock walnut or beech?