I'd hazard late 70s and maybe even early 80s, due to over BB cable routing and clamp on gear levers combined with allen key rear brake fitting. Unless the latter is a later frame drilling. I have a 1982 frame built by Steve Roe (ex Falcon) that has over-BB cable routing and non allen key brake fittings; some builders stuck to the old ways into the 80s. The forks are not original, of course; if you want it period-correct, you need a nice pair of 531 forks.
Difficult to judge the "level" from the pics. Are the rear drop outs Campag? If so, then most likely a good racing frame. If lesser (e.g. Gipiemme), then more likely to be a mid-range frame. I'd guess the latter, as the lugs and brake bridge are pretty plain. But what really matters is how it rides, of course.
I grew up hanging around HH's shop in the 70s and used to lust after a HH frame. By the time I could afford one, I'd cast my eye further afield. Still tempted to get one for old time's sake...
Nick