Doing some digging for takara's plastic rules, sadly they used a flash based site from 2003 onwards so it's hard to dig up the final sets as there's no clickable link to them (the worst thing about that era of flash sites, and there were a lot of horrible things about those flash sites), and the previous site's rule list is the same as the 2001 one, and hasn't been updated for the bearing gyros AR legalisation that apparently occured.
But, digging through that earlier site, I found this:
http://web.archive.org/web/2001061907004...index.html
The bottom middle picture and the text for it indicates the AR's of those hidden spirit beys were intended to be legal, while the BB/Weight Ring weren't, unlike the later designs where they used proper weight disks and four-layer style blade bases which I'm yet to see any indication of illegality of from takara stuff.
Also found this:
http://web.archive.org/web/2005011115344...st/12.html
Which is supposed to be #12 Spark Disk, and matches the images of it in the spin up guide book. This clashes with what Beholder said about it merely being a Wide Survivor with flint and sandpaper (and wide survivor does have holes for flint). Looking at it, if that is spark disk then I'm wary of the legality. Early versions of the takara rules at least very clearly banned it, and all of the bearing gyros parts including the AR, though the bearing gyro AR was unbanned later apparently (part of me searching for a later rule release).
Back to digging...
EDIT: Looking through all the archived pages and haven't seen the rules page. Gah.
Though, I have got the links for the part lists, which will let me check a few I'm not 100% on, I guess, but then given there are very obvious errors in the coro coro parts list (calling Cyber Dragoon's SG a NEO SG) I wouldn't be completely shocked if there were errors. Will look through it later, getting tired. EDIT: They got cyber dragoon's sg name right, so I guess I'll go back through beywiki's parts list to check again lol.
Image of spark disk in the parts list is dead and there's no mention of wide survivor. The spark disk filename is sparkdisc.gif, with a C, so maybe it is spelt that way, however there are a lot of poorly romanized image and page names soooooooo
Oh, and the site's page on Fukobako 2003 page basically confirms that Ortros/Ortrus didn't have blizzard in the name, seeing as it doesn't use 'blizzard' in the name for it.
Also an interesting note about the guide books, while they're a great resource they do contain errors. Kerberous is clearly romanised as such on the BK box, but the guide book has a large title saying "CERBERUS".
Apparently one of the Spring Launchers (I assume the actual Spring Launcher (A-4)) apparently uses a 9-tooth gear, like the EZ Shooter Power Custom. I just won one on ebay (incredibly lucky timing) so I'll check that out I guess, and here's hoping.
Lastly, the part names for two-part attack rings are Core Attack Rings and Sub Attack Rings. No idea then what the heck they call SG Wing Base's Sub Ring part but they never name that separately from the base.
EDIT 2: Duh, just realised the rules are on every instruction sheet. Honestly from the rules I've seen thus far apart from Gyro Beys and Spark Disk being banned and Hayate etc's AR being the only part of them considered an actual legal part (unlike the other hs beys where all parts are apparently legal), there seem to be no rules other than a size/weight limit (that was increased by 10g in 2004), only one weight disk, and no modification of parts, addition of external substances OR addition of metal balls, i.e. "use official parts and then throw them together however you like and if it stays together, it's legal!". Personally I like those rules, heh.
Really, I was actually hoping they had a full ruleset somewhere that covered more specific things, like SAR inversion and what tips can be swapped and so on, whether you could use a base without its tip, but I guess they didn't make one. Bleh.