When I went electric I used the blanking plate from a mini, a couple of quid on eBay. I used the fixing holes to attach a bit of strip to mount the new pump on, has worked well for a few years now.
I use the overtaking mirror as mentioned above but find it better horizontally rather than vertically. It has fallen off a couple of times but they seem quite robust, so I’ve just been able to retrieve it and refit it.