Yeah, they are still on the NFA. So all other rules around them apply, such as the application process with the ATF, fingerprinting, etc.
The other commenter mentioned above that this does open legal challenges against this portion of the NFA, however. As gun registries are illegal and if this is no longer a receipt of tax payments...
Do not, absolutely do not, hook an OS that is no longer receiving security updates to the internet. Out-of-date machines can get pwned simply by being on a network or loading a website's ad, no user interaction required. Vulnerabilities are discovered, never patched, and thereafter every script kiddy can get into the old machines with little effort.