My congrats on the new conversion on the No.1. A most exciting time I am sure.
I think you will enjoy it. The moving of the firing pin mechanism within the breechblock is the more elegant method to some, others perfer the shortened breechblock arm. Keeping the original barrel exterior appeals to many too. I took the easier? way out, I put on a Shilen rimfire barrel blank contoured by me, refitted the quarter rib, and made the shorter lifting arm from scratch. The extractor is not that bad to do really.
My rifle kinda came out like a No.1B in appearance, not as close as yours cosmetically with the original barrel, I assume chamber plug, and liner. Yeah, it is fairly heavy, but these type of conversions have their own elegance and admirers. I have a couple thousand rounds thru my own rifle now, shoots ok, and functions like it shoulda. On my rifle, the trigger really needs work, way....way...too heavy.
You are lucky, I never could convence any of the local guys to do the conversion for me, so had to do it myself. There was some ups and downs in my process, learning and fabricating; but we got there ok.
Perhaps someday we will work out the breechblock firing pin mechanism to work with either type of case(rimfire or centerfire), with a simple firing pin replacment; kinda the best of both worlds.
Hope you will consider posting picts of your new rifle when it shows up and you have the time.