Hell All, I also have a 3v that is my favorite rider. I have this set up with a 50th Campagnolo Gruppo and on most rides less than 35 miles it is my go to bike. I have at least 5,000 miles on it and the ride is strong and firm.
I also have a NOS frame is box that is gold in color and also carries the Cyrillic lettering and the pictures of the Olympic flags of the different nations that MASI participated in. I hope to transfer the Campagnolo Gruppo to this frame and install a less risk gruppo on my rider.....
In addition I also noted the request for info on the Cyclo cable setup. I have this on my early 70s Alex Singer, I supplied the complete kit to him and asked to have the frame built in the "early" style.....If your cables are correctly double wrapped around the shifter then you should be able to tighten the cable at the rear using the small wire nut to increase or decrease tension.
Best of luck,
As a longtime reader/member and a new participant please forgive any boo boos in the message
US of A