Vizard makes some excellent comments in the Mini book about the factory turbo Metro, and how the fuel curve under boost can be addressed with a simple fabricated part in the air-horn.
I'm not sure how to run the plumbing, but you're inviting fuel drop-out by running plenum volume after the carb, especially if the X-section goes up. You may find yourself with a wet cylinder due to droplets running down the easiest path, and trying to jet lean to dry it up, etc.
I'd rather see storage before the SU, and short entries.
IMHO since the plenum volume is a buffer (not flow capacity), it need not be in-line with the compressor discharge to air-horn path, but can be suspended in parallel (as long as the connection is large enough, larger than the area of the main transfer with radiused intersect), or even a bottle. This last allows very rapid plenum vol changes, like for dyno work.
(wrestling with my own junk: H-D side-valve twin, 3-7/16" × 5" with chain-driven M-45 and single blow-through CV)