Didnt do anything with the cilinder, transferport and taploader on mine and theyre beautifull to shoot recoil wise. So I dont see any issues with those. They seem to be far better designed than the later Webley taploaders (tracker, osprey) which are/can be, kinda harsh to shoot even after tuning.
Id start with a modern well fitted, modern pistonseal and work from there.

Checked out the tinbum site btw, didnt see any Webley kits on there. I doubt there are any kits (left) for oldies only 'springs that happen to fit too'= universal. Those will never give best results.