I had a look at the newer technical service Autodata 2012 manual I have but they don't list ratios unlike the older ones which gave all the gear ratios plus the number of teeth etc.
I do see that Haynes manuals gave some detail so maybe if all else fails that may give you a guide.
It does seem to be hard to get much data from later Haynes manuals, mostly good for oil change and spark plug DIY basics.
As an apprentice we used Technical Service Data by Palgrave Publishing which gave lots of detail, they were superseded by Glasstech which were OK but then AutoData took it on and you got less information unless you subscribed for online service, but I have retired so not a good investment.
final drive ratio on a Punto 75 is 3.733:1 which comes out as 56/15.
If you have any ideas about modifying final drive ratio I have to disappoint you - the pinion gear is one piece with the shaft it's mounted on, it cannot be removed or replaced. Best solution is to swap the whole transmission for the one with wanted ratios
The Grande Punto gearbox needs dismantling anyway as there’s a problem with the 3rd to 4th gear change. Plus I think the clutch on the 75 is cable operated and the GP is hydraulic.
But I still need to find a 75 gearbox in any case…
i believe that clutch actuation can be converted if you have both complete gearboxes. You need to transfer release bearing arm (held on the shaft by a clip) and gear selector housing that carries the slave cylinder because i don't think the selector housing from a cable clutch gearbox has the mounting holes for the slave cylinder (maybe it does have the holes but i don't think so). All that is still a lot less work than doing internal work on the box.
Also I think some, if not all, RHD mk1 puntos had hydraulic clutch so maybe no work will be needed.
LHD market mk1 puntos have cable clutch, maybe some don't but i haven't seen one with hydraulic yet.
You will need to transfer speed sensor. It's electric on mk2/mk3 and spinning cable on mk1.
Maybe you find some other mk1 punto gearbox.
55 has a similar final ratio of 3.866:1 (58/15) and a mk1 60 has 3.563:1 (57/16).
Punto mk2 6-speed is also a great candidate with a final drive of 4:071 (short final but you get a 6th gear of 0.766:1) and it already comes with hydraulic clutch and electric speed sensor. It is available on mk2 sportings, 1.2 16v and 1.4 16v, both cars have the same gear ratios.
I don't know if there are any other differences when putting older gearbox on a grande punto but i think this is it.