An older M 15 frame would be just the thing. But, I assume the number of handguns to select from is rather limited in Finnland. It seems a shame to use that M 14 since it is such an outstanding and desirable handgun.

None of these swaps like this can be counted on to be "drop in" jobs. Most likely the cylinder will have to be 'fitted' and for sure the barrel will require gunsmithing. And, the barrel might require extensive work like being set back one turn. Then the front sight could require being altered to a new height.

IMHO, you should continue looking for that 'beater' M 15 and then hope for the best. .....