This one's got me mildly fascinated!
The Gran Sport decal on the downtube is clearly the model name, but Gran Sport doesn't appear as a fully built model in any of the Bianchi catalogues - unless it was a USA or Japanese model (for which the Registro doesn't have such good records) - where are you based
@zrudeboy?
The closest we get is the Gran Sport frameset which was around in the 1960s. See 1960 Bianchi Parts Catalogue scan, below.
View attachment 736245
Which would also fit with it being described as having a Simplex rear derailleur originally, as factory-built bikes were almost exclusively Campagnolo in the 1960s. So it feels like a built-up frameset bought through a delaership and built to the original owner's spec.
The frame is a really interesting mix: the chromed ends and lugs are really nice. The headbadge looks like the rare, mid-60s spread eagle on a cream background:
View attachment 736248
The headset and cottered cranks are suitably 60s (side note: try to find a suitable pin spanner to adjust the headset, don't resort to plumber's or stilson wrench!) while on the other hand the rear dropouts look pressed rather than forged and the seatstay caps are quite abrupt? So it's a mid-range mix of really nice features with a bit of cost-saving thrown in, which, again fits with built-to-order spec.
The stem, of course, is an abomination to a purist but an immensely pratical modification to an owner who is perhaps not as flexible as they were back in the 60s, loves the bike and wanted to keep riding it. Good for them!
Some drive-side, head tbe and bottom bracket photos would be great, if only for vicarious value - it's a cracking bike that will be an absolute hoot to ride.
