Custom-fitting both the main pontoons and top wings turned out to be all about finding/bashing the best-fitting PE struts:
Installing main pontoon struts, so far only on the pair of silver-painted demos, the trick of leaving a single peg from the original casting (clearly visible on the blue-gray one, at lower-right), for use as a temporary anchor, did again work just beautifully. While difficult to see here, 500-scale "X"-braces were used (though I realize the cross-members are a bit overscale), as these essentially doubled the strength of the attachment. This method - not yet completed on the silver pair, and barely started on the blue-gray duo - can already be expected to be highly successful.
The same could not be said of the first run at top-wing attachment, as started before pontoon-attachment on the blue-gray pair - the first mistake in itself, right there. Far better to attach the pontoons first - not to mention also to paint the canopy framing (before the top wing gets in the way...Duh!). Besides which, I had quite a bit of trouble fitting the main "N"-struts - as can be seen both in the purple, scraped-clean spots as well as large CA-glue blobs - before adding any fuselage-to-wing struts, also tiny "N"s (not shown). So I will pop all these off and (clean/resurface and then) redo the top wings the right way - although this trial attempt has been invaluable in precisely identifying/fitting the optimal parts.
All the SOC's struts can be glimpsed on one or another of The Real Things - a full quartet of them - photographed astride USS Pennsylvania on July 2, 1939:
Click on Image to Enlarge
The proof, to back up the above, coming soon...