#2..I'm told the older Siler & the newer Siler use the same internals.
#3.. If the blind holes in the lock plate are already tapped and everything lines up nicely with an already installed side plate,,I'd probably use the 8/32 side plate screws and fit them to the blind holes..IF..the depth of thread is sufficient to secure the lock in position.
You don't want the threads to strip out after a few tightening sessions of taking the lock off and re-installing.
The blind holes are a nice cosmetic touch,,but not at the expense of real world use.
I use 10-32 for side lock screws many times too.
#4...I don't really care for the staples,,but again if everything is installed and lined up already, why create more work. The length of the slot has nothing to do with anything. The stock or bbl isn't going to slide around. They're secured together at the breech.
I'd sweat solder the posts of the staples into they're staked holes as extra precaution,,but that's just me.
If I used them myself,,I'd add that extra step,,but I don't use them.
A bit of flux, bring up the heat and touch the soft solder wire to the joint and it'll flow right into it cleanly.