A perfect summary - I know from experience - I've tried and failed !!!
If you fit a 5C you cannot use the BA21 and scope rings.
If you fit a 5E sight then you can use the scope sight rings but you cannot use the safety.
The answer is - get hold of a 5E sight and make a new shortened safety (you cannot buy one - they are at least 10 shelves above rocking horse poo & hens teeth)
Thank you Alan for the perfect summary.
I wonder if I could find a 5E to buy or trade for a 5C??
Worse case scenario, I will have to fit or remove the 5C if I want to enjoy the peep with the excellent AJP MatchMaker front sight system, or the glass system.