Canvas scans, stacking, stitching, stupidity.

[Kirra Kent]

Hello Hugin humans, I am desperately hoping you'll have a solution, a tool, or a tutorial to point me towards?

Issue/info: I am scanning and stitching a large canvas together; it has been scanned east, west, north, south. There are just shy of 200 files, approx 35-40 per direction. (I use a 17" x 12" Epson 10k XL flatbed).  I have separated the scans into directional folders, but the distortion within each scan as an individual might make stacking after stitching difficult?

Normally, I don't need 3 - 4 rotations to get excellent reproductions, but this painting is so dark that the canvas gloss is causing more issues than usual. Each direction has a tiny bit of distortion due to the scanner edge; I did everything in my power to compress the surface as flat as possible. 

 I have separated the scans into directional folders, but the distortion within each scan as an individual might make stacking after stitching difficult?

Goal: Stack and stitch scanned panorama, ideally simultaneously. OR Stitch then stack, without distortion causing detail loss in overlaps.

My PC is relatively robust, so computationally heavy but effective solutions are welcome. 

I completely understand I am being a certified dingus with this, but I don't have space/money for a canvas photography setup; I am a freelance illustrator at the start of their career!

 (plus this method has worked for the last two years (hugins high score is a 72" beast, beautifully stitched) ... this one painting is kicking my butt)

Currently I have tried:

Hugin searching through all 4 image directions (set focal length to 1000, I read somewhere that makes read as a flat image)  (geometric positions, and Hugins CP find for feature matching). (still not done)

Affinity Photo 2 -> crashes out from uber image stacking.

Auto Pan Giga -> Introduces distortion that makes stacking in post impossible. Its like it selects the over exposed pixels, have tried multiple render outputs on this bad boy.

thank you for your time, consideration and anything you can offer me.