Gareth was kind enough to send me a picture of his hub:
Pulstar hub
This is my Diamondback hub:
Diamondback
Not the same, but some similarity. With a cheap HarborrFreight caliper, I measured the smallest part of the Diamondback hub 1.0675", and where it first steps up, 1.221". Is that close to the Pulstar dimensions? Any hope for a clamshell adapter? No doubt I'd really like one.
The build is going to be the HarborFreight 80cc 2.5hp rack mounted, home made aluminum rack, Bulletlines TAV2 clone CVT, jackshaft with about a factor of 2 reduction. The CVT has a 10 tooth sprocket. The rear wheel sprocket would be 56 teeth if I use a 2:1 jackshaft, but instead I'll probably go down to a 44 or 48 rear and adjust the jackshaft ratio accordingly.