You'll have great fun when you take a swing with such a rod!
First: You'll find line general weight recommendations for the switch rods in this forum.
IMHO the grain weights stated, indicate what you should use as a minimum for "single-handing" ("low") and as a max for "double-handing" Skagit-style (high)
Line weight for Scandi style (underhand casting)
For the Scandi style, you must go slightly lower than the high indication.
A #7 (which I use for Scandinavian Seatrout and Atlantic Salmon), 21 g (grams) is Perfect!
For the #8, approx 23 g should do the trick!
Shooting Head length
For Underhand casting with 10'8" and 11' Switch rods: Keep the heads short!
Max 30' - could go 1 to 2' shorter, depending on density.
Shooting Head Front taper
As long as you like, but making the front taper "not too long", you'll get more degrees of freedom when adding a polyleader (better turnover of the "heavy" polyleaders).
Airflo 10' Steelhead/Salmon (or the 8' Seatrout version if you can get it) or similar.
For floating heads you can use everything from Float to Fast Sink versions with ease (incl. tied/tapered mono leaders).
For intermediate / Slow sink heads, you just exclude the floating polyleader.
Fast sinking heads (Sink 3 to 4)
Fast Sink or Super Fast sink polyleaders.
Approx 5-6' for Float and intermediate - can be longer.
"As short as possible" for sinking polyleaders - you want to keep the fly fishing in the depth defined by the line/leader combination - not fishing "somewhere else" in the water column!!