I would also have to think your 608 would still have its original 6-blade fan (being this one is an '87 model), rather than the 9-blade fan used on 1990 and later models, right?
About that bag: that is the same one that the model 611 (fifth vacuum to right) is pictured with on the Royal Service Folder.
Yes, as did all Royal Heavy Duty Commercial uprights (with the Adjust-O-Rite) made between 1985 and 2002. Prior to 1985 or 1986, the AOR plates still had pull knobs a la the household type models.
I'd think that the Adjust-O-Rite originally on your 608 had a black plastic pull tab, right (like the one seen on this 654)? It should've also had the "HEAVY DUTY COMMERCIAL" decal with the Royal logo marquee on top since yours was made in March 1987 (and Royal first used that decal on its commercial-line uprights in September 1986).