Yes, you absolutely do need an HQL, and you still need to go thru the regular 77R application process. Under federal law a pistol frame is the firearm, stripped or not, and there's no getting around that. That's why every seller on GB that's selling stripped Glock frames requires an FFL before they'll ship it anywhere.
Yes it is the firearm (hence the xfer fees), but it isn't necessarily a pistol. You could do a rifle build with it and therefore not need an HQL. This isn't the first time this topic has been discussed, so I won't make any more posts on the HQL requirement.