That is on very big bass. I have an
old English Bass (attributed) and yours is even bigger. Mine was just restored and the block area cut so it's slightly smaller than before but still, yours is even bigger than mine ever was.
Please tell me what the string length is currently with your altered bridge position and if you can. lay the bass down, move the bridge to the center of the f-notches and tell me/us what the full/intended string length is. Also, what is the depth of your Ribs NOT including the Top and Back plates? Please measure them at the bottom Block, each Corner Block and up at the Neck.
For easier viewing, I will post your pics here from that link above;
Looking at the Scroll, I see some 'fleck' in the wood at the upper turn under the extension. That looks like Beechwood. If the Scroll is original to the Bass (and that's a big IF) then I would place this Bass in central Europe, maybe!
I think people in general have narrow minds when it comes to origins. If Violin cornered, then pick Italy, France or England depending on the style of the Bass. If Gamba shaped they pics Germany, Czech or Austria. Maybe they are right some of the times but that doesn't make it fact as far as style and school of making.
There were Basses made in Spain, Portugal, Sweden, Ireland, Scotland, Belgium, Holland, Poland, Hungary etc, etc, etc..
It has a Guadagnini label? Can we look at the label? Which Guadagnini? There were several makers in the family.
Basses like yours which are quite large (not the biggest I have seen) are usually considered full sized 4/4 models. I have even heard them called 5/4 by one shop in England. Just because there are larger Basses doesn't make this less than Full sized. Some of them with Top lengths of 54-56" are 'oversized' basses like 6/5 or 8/4 in my mind, like Lumber thickness measurements.. lol
Like a Car, a Full sized is a 4-passenger sedan. A Stretch Limo that holds 12 is NOT the Full sized one knocking your down to a mere 7/8ths.. lol
I briefly played one of two Basses yesterday in NY that are labeled Giuseppe Guadagnini. The Varnish was similar to the color of yours but these were 7/8ths sized (or 4/4? depends on who you ask) Violin Cornered Basses. Only one of the two has its original Scroll. The other has a replaced German Scroll which looks nicer than the original one. The Basses are nearly twins. I don't know the exact dates from the Labels but c.1800 or so for each.
Do not rule out Italian for your Bass and equally, do not rule out several of the other countries listed above either. A careful internal examination of the Bass might help include or discard some of the origin possibilities. Some people as mentioned are just too quick and narrow minded when placing origins by style alone of a Bass.
On mine, you could ask me how did we come up with English. We have
discussed it here and
the bass listed here. From Europe and USA I received several possibilities but most were guesses. When the English dealers saw the pics they all, not just some but ALL said it was Northern England, 19th century. Well, I see how they came to that but the FFs are way more refined than what I have seen from the Northern area makers like Tarr from Manchester and his followers. I have seen London Basses with closer resemblance so I think it was the Gamba shape that thru the opinions 'out of town' so to speak..lol
What they didn't see or anyone else see is the inside and a close look at the Purfling of the top and scratched/painted lines in the Back. Combined, they point to 18th century London from what I have read but that's just the outside. The Corner Blocks are Northern Europe Furniture style, England and France from what I have been told. The Top Purfling shared by both countries as well. In the lower Back we see the oldest Cross bar scars of twin rails. Gamba/Violone style making. The butt of the Neck heel was attached to the current Neck and that slid down behind the 'current' non-original Neck Block which was a dovetail. That butt piece that slid down into the Back is a remnant of a Blockless neck. More evidence of the period of early English Gamba making. These are a few things that were not at all known without opening the Bass. When the dealers here in USA were trying to guess the origin, many of them said Germanic or Bohemian fro,m looking at the Dovetail alone. I currently own 3 Italian Basses that were made originally with a Dovetail Neck/Block. So there, it is NOT exclusive to Central Europe. I am sure you can find this in England as well as Blockless necks, Blockless Corners and even Cornerless in the Violins at least. Don't forget the Nails either. Even Strad nailed his Necks from the inside for extra support.
So, Gamba, Big, must be from the Tirol because you can't pin a German maker or School to it? Nahh... Think again.. open your mind. No one, not a single country in the world that made basses OWNS the Gamba design. It's public domain.
Nice Gears by the way as well. Any idea what they are? The ones on my restored English Gamba look similar but I know now who made them. It was 'Fawcett', the maker of the English C-Extensions. The Gears are about 20 years old and have been in-stock un-used all this time.