Jeff, 
From the measurements I took and compared to dimensions that Wal has in his book on the Webley it is considered a medium action.  I believe with the 1" or 1-1/16" threads it would handle a 470 NE.  Not an everyday gun but definitely comfortable when walking among things that consider us edible.

Gil,
Squaring up a new block and make the mortice to fit may handle a Krag or a Zipper better.  There is a lot of meat behind the block on this and getting away from round and giving the block support like a HW would be positive.  Stress calculations would be something to look at.   You'd have a "rook" square block when you were done, haven't seen one of those before.  Keep us posted.  I may have to do one of those now...
On another note, the "straight on firing pin", the transfer bar, and flat spring from a Chevy are working well.  There's no shortage in positive ignition at least on the 22rf.

I thought the hammer would reach the transfer bar so i'm glad you did all the experminting so i can jump in with both feet & be right on first try. Thanks

I had considerable carnage getting to this point, I have the process on the run for the moment though.  I had looked at a fp like TC uses, and switch barrels, but it's more involved than I'm wanting to do, I'll just build another rifle.  I have a CPA and a couple barrels and breech blocks - I can count on one hand how often I've switched setups - just me I'm sure.
This is my rf build and up next is at least one cf build.  The T-slot method of pin retention needs a little refining yet and vent hole location determined.  I think it will end up with the pin in line with ones face and this is still a concern.  On the 22 there is still the rear of the action blocking this, not so sure with a CF.