(just getting back from an out-of-state-trip...and reading your questions).....
To answer your questions:
This would depend on what Blanks you are going to use....and amount of "funds" available to both "Blank-Adapt", and buy Blanks.
....and last would be "depending on what you want your MG34/SA34 to sound like"....your noise level requirements.
(NOTE: You will still need the modified feed-tray due to the MG34/SA34 having issues with feeding.).
Are you going to be using "hot" or "standard" 8x57mm Blanks (?).
.....or .308 "surplus-blanks" (7.62x51mmNATO)......and again, made by who (?)....or are you going to make your own (?).
Basic guidance would be:
1: If you are going to use "weak-blanks"....then go with the two-pcs. Blank-Barrel-assembly because is requires less pressure to operate........."but" it does cost more-$$$ .
2: If you are going to use "hotter" Blanks (or are short on funds-$$$) then the restricted booster-cup/"nozzle" will work and is cheaper......."but" it does have a few draw-backs as I talked about earlier.
Give me a little more information and I will be able to help with better answers.
Maybe with photos of the blanks used/feed-tray-modifications/any problem-areas that you are having when you get started.
(NOTE: I will not go into "loadings"/making Blanks at this time. Please don't ask.).
Regards, RichardS in MI.Blanksguy2001@chartermi.net