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.