Thank you
Sandman0077 for putting that triangle together! However, as it happens, the "geometrically perfect" version with one segment copied and rotated 3x doesn't actually line up with the original quite right. I don't mean to sound unappreciative, because you created exactly what I was asking for, and it looked great on its own!! But it turns out the original must have been hand-drawn all the way around, since there was a bit of inconsistency to the spacing/angling of the hatch lines in the three segments.
To that end, I've had an external conversation going with
ThreshKeller, who has very graciously hand-drawn the entire triangle graphic--and who has encouraged me to share their images here, in case it's useful for anyone assembling their own covers. It definitely lines up with the graphic on the original scan, and I must admit there's a subtle organic
je ne sais quoi to the hand-drawn asymmetry that appeals to me.
www.dropbox.com
If anyone happens to have a lead on a higher-quality version of the author portrait from the back cover, please share here! Currently that's the lowest-quality part of my cover and
ThreshKeller is helping me to improve it...but a higher-res photo than the original scan would really do the trick.