Sadly, I don’t have a ton of information on this model. I stumbled across it on a Small Arms Illustrated page and poked around online.

The most complete information I could find was a photo of a snippet from a book:

Text from the photo:

Left side closeup of the final 7.62x39mm Finnish prototype, produced for trials in 1960, showing the unique features that it and only it embodied. This one-off was produced from a standard lower receiver with a modified magazine well, cut through the middle of the existing standard manufacturer’s markings and retrofitted with a magazine guide behind the new, curved magazine.

The charging handle extension lever was reversible from the right to the left side, based on shooter preference. Note the flat-topped carrying handle, rounded at the rear to protect the rear sight, fitted with a range scale modified to fit the trajectory of the ballistically inefficient [🇺🇸 🇺🇸 🇺🇸] Soviet round.

All of the remaining parts of the rifle, except for the chamber and actual bore diameter were identical to those of the standard Second Transitional carbine.