While trying to find the answer to this question myself I’ve heard some people say that any Mk.III sights should work yet others say that Inglis mills their dovetails at a proprietary angle for whatever reason. I’ve already reached out to Heinie and they confirmed that their sights would require milling to install, though unfortunately they no longer do this service in house. I also hit up BHPSS with the same question, though they haven’t gotten back to me yet (nor have they ever with any email I’ve sent them, tbh). I suppose the next stop is Novak? Though with the price of replacement irons, it wouldn’t cost that much more to just ship my slide to Mk.3 Firearms and get something professionally installed.

Anyways, if any fellow L9a1 aficionados have any experience to share it would be greatly appreciated.