Bleh, but kinda confirms my point too. I do think there are some 3-rail setups in other border regions though? I should check… then again it doesn't matter that much if it's 3 or 4.

As for the loading gauge, yes, of course. On the plus side, this is Finland, most of the lines is in the middle of nowhere and single track even. Maybe the best option for them is to just build 1435 in parallel whereever possible, and just merge where not otherwise practical (bridges, tunnels, populated areas & stations). I don't even think it's that infeasible considering Finland's layout. I'd wager there are only a handful of specific locations that need expensive work.