you don't weld on the struts themselves. they are inserts that you remove before welding on the strut housing itself.
as for how low you can go, i think 2"ish is about all you'll want to go on stock length strut housings, otherwise you won't have enough travel before slamming the top of the strut housing into the top spring cap.
I'm about -2.5 and I hit the bumps on the regular...and that's with a stiffer spring than 2b offers. Same sleeve setup, but even lower on the housing than the normal way:
pages 2 & 3 have all the strut stuff
The rears are not much of an issue but I suppose if you wanna drag the pan around they would also require sectioning
After wuste i'll probly make like a 'cuda and section some front strut tubes
I still can't recommend lowering these cars that far without some other serious mods to the suspension geometry. With my car dropped about 4", the handling is T E R R I B L E. Darty is an understatement. It takes away the nice notice you have before the car gets upset and becomes a handful.
The only way to remedy it is to adjust the control arm mount points. Inner control arm mounts need to go up, or ball joints need to go down. Plus the tie rods as well.
my $.02 anyhow