PLEASE do not make any alterations to this rifle. It may not be worth a fortune but it is very rare and valuable as piece of history.

If you want a hunting rifle, a truck gun, or just a fun shooter or project gun, there are a MILLION other Lee Enfields out there that are available and have no collector value.
Heck, I would trade a you a No.5 Jungle Carbine that already has a scope mounted (on a swing mount so that you can still use chargers)---this is a bubba classic: flash hider removed, Fajen stock, scope already installed. Ready to go. There are a bazillion such rifles out there. They are fun, they work, they have taken a million deer---but your No.3 Trade Pattern Carbine is NOT one of those.

Just to answer your question: there is no charger bridge that simply screws in. To make something like that would not be cost effective, and would ruin this carbine.
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P.S. Got your latest group of photos of the butt and nose cap. I'll post them to the forum as soon as I can.

Cheers!