Lots of these things around, and they tend to get used and tossed. Instead of seeing them as a "disposable commodity" because of that seal on there, or as something never to be opened, I think it's a good thing to see them as raw material after they've served their purpose in sealed motor racing. With quality vintage parts *for either D or C-sized motors getting pricey and rare, the good old "modern D" can be seen as a modified Champion or Mabuchi. They already have strong magnets (no need to search out shims and aftermarket period magnets). The cans have already been cut up for clearance and weight, and you don't have to jump through a bunch of workaround hoops to hopefully not have the endbell melt into a puddle of acrid-smelling and smokey goop. I kinda like the oval hole Deathstar motors, but these ones work fine for all sorts of stuff. About the only thing you couldn't easily do with one of these (although it wouldn't be all that hard) would be to mount it endbell-drive, but who wants a serious performance motor to be endbell drive anyway
So, I'm going to build one of these things up and not do much at all to the basic package. What would be the use afterwards? Well, it could just go into a modern fun-racer, but it could just as easily go into a vintage recreation build... one where every other detail is as vintage as possible except for a pricey and hard to source vintage motor. This would not be at all some sort of alternative to "Retro", just a way to have fun with vintage without making things more difficult than they need be.
On the other hand, it could easily go into a modern Retro chassis for fun (although not sanctioned) running/racing. So, lots of people have parts and modern "junk" lying around. Save that stuff because it's "raw materials." I'll have one of my arms "in the chamber," but there are gobs of off the shelf arms that could go in there as well.
Time to get building.