This seems like the perfect project for an Origin8 Bully frame if you can find one it has a long wheel base and very good geometry. The horizontal dropouts would suit your IGH better than it does my derailleur setup. That low BB on the giant would kill the ride for me, 90% of the fun of those hookworms is laying the bike down in a turn but keep up the mini velo realness!!! It does seem like the best frames for a bike like this are for the most part on the other side of the planet, something like a mercier nano is cheap but the wheel base is too short, i know they arent avaiable here but look up the doppelganger 530 or 555 or look up the wachsen BV-207.
P.S. those wheels are CRAZY! Too rich for my blood but neat they must be a great conversation starter if nothing else.