It turns out that Shorai makes another version of this battery, the LFX36L3-BS12, that is exactly the same, except it has the opposite polarity of the one in this DIY.
If you used that version, you would not have needed to make adaptor/extension cables, and it would have been a drop-in fit.
http://shoraipower.com/lfx36l3-bs12-p130
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