[Kos-Mos]

Then you have a very simple choice:
Bring you 4.3 to a gundoc that know what he is doing.
You won't screw parts and he will probably be able to fit a 5.1 part if need.

You can also install a complete 5.1 4" slide kit with 5.1 sights and cocking handle.

Or have a 4" built from scratch.

But if you want to whine and bitch about a non-issue, you have chosen the wrong forum to do so. People here try to find a solution, and in this case the solution is very simple. If you can't accept that and want to be fed your very own custom solution, try somewhere else (for example a local forums, seeing as you are 1000s of kilometers away from here).