I've machined a few hand-fulls of stock sets for them in two "English" styles with a pistol grip butt-stock, which has given me an insight into how several of them turned out.

Research barrel profiles thoroughly. I've seen a few built which were too light, and a few which were way too heavy. Try and achieve the desired weight, and the right balance. Obviously there is a personal element to all that.

Most of the lever conversions I've seen subsequently done, are a bit of a letdown (literally). Levers not let into the grip, not well formed, and not secured by whatever means.

There are nicer ways, but a quick-n-dirty means is to sneak a suitably sized rare earth magnet into position, secured in the grip, and watch folk try to figure out how the lever comes home so nicely! Too big a magnet = too aggressive and noisy. These rare earth magnets last and last, and they are super strong for the size. Worth considering.

I say that because the levers are rarely re-worked to be a nice fit, inlet into the grip. Time, money, or what-have-you - and to go to the trouble of securing the lever seems rarer again.

The second simplest way, I reckon, is to employ the original lever latch design (suitably modified) into the back of the lever. If the lever body is inlet into the grip it's only visible when the lever is open and it's a reliable system.

I've seen a few levers inlet into steel grip caps with an interference fit........with the lever and cap hard they work OK, but will eventually wear and if it's the only attempt to retain the lever, not a real good idea IMO.

As with barrel profiles, choose a blank of suitable density if re-stocking. Less work when it comes time to balancing.