The hoods are notorious for cracking/buckling in front of the hinges. I would not suggest gas springs unless you reinforce the rails along the hood.
Jake was making some of the firewall grommets and other 521 parts, but I'm not sure how active he is anymore:
Everything points to driveline - something is kinking under load and relaxing on coast. Speed related, but goes away or lessens without load, so not likely wheels or axles.
Not to be "that guy", and maybe it doesn't really matter, but the grease seal isn't supposed to be in that far, I believe. Pretty sure it's just supposed to be flush. Some drawings even show a spacer between the bearing race and the seal, but mine for sure didn't have one...
Their first Z rear setups were sketchy IMO. They've changed the design now it looks like. Before they basically had one heim in shear holding the whole thing in place. The 510 rear setup looks decent
Spoof? No need, just fake or hijacked accounts. Always ask for additional pictures, including pictures with a handwritten name/date paper with the item(s). You'll notice these scammers selling lots of items where the background/backdrop is never the same, because they're stealing pictures from other legitimate people.
Scam 100%. Join Datsun Parts and Needs for a legit group, and/or Datsun Classifieds
https://www.facebook.com/groups/327981873903624
https://www.facebook.com/groups/464479646940228