Scott, I happened to run across the attached ad for your C-450 from the June 12, 1978, edition of THE BANGOR DAILY NEWS. Others I located were from 1977 to 1980, so it was one of the last Premier Swivel-Tops if not THE last made in the U.S.; the Canadian ones were manufactured until c.1984.
It may be that the "Whirlwind" name corresponded to the 7A motor versus the 750W (6.25A) motor of the attached eBay photo of the gold-colored G-E Swivel-Top C-350 and likely others.
Attachments
1978 Jun 12 BANGOR DAILY NEWS - Premier Whirlwind canister vacuum C450.png