The Harley-Davidson plan (as announced) is not encompassed by my understanding of the word "spin-off". It's completely different thing. The new company will still be owned 74% by H-D and HOG shareholders get no separate stake in the EV division. Essentially, H-D is capitalizing their EV division by selling some of it off. Shareholders actually end up with less interest in the EV portion of the business than they do now. But that's considered fair because the division has more cash with which to use for R&D. It's considered that shareholders have traded some of the EV division for cash and the SPAC shareholders have taken over that interest. That's how the deal is described in a nutshell in the press release.
In a spin-off, shareholders end up with new shares in the business that is spun-off. That's how I became a shareholder in Leap Wireless at no cost to myself and was able to sell the shares after the spin-off for "free money". Leap Wireless was spun off from Qualcomm. In this transaction, HOG still owns 74% of the EV division and shareholders get nothing except for a smaller share of a re-capitalized EV business. Someone please correct me if I've over-looked something because I have not done a deep dive.
If H-D investors really believed in the potential of the EV division, they would stop this transaction because the money needed to re-capitalize the EV division could be raised through more traditional means and carried as debt thereby leaving HOG shareholders interest in the EV division undiluted. That conclusion is debatable depending upon whether you think the EV division will be profitable enough eventually to pay for the debt, but this is not a spin-off and I don't expect it to have any predictive value as to how a more traditional spin-off by Ford of their EV division would go down if they actually decide to do such a radical thing.