I was going to take a 172 to Slovenia from FL October of last year, but it broke down enroute to maine. Never did get to finish the trip.
We were going to go Goose Bay - BIRK - Wick route, which should have been able to keep us in VHF comms, even a piston single, probably at at least 10,000 ft as mentioned. I have done St Johns - BIRK without HF, but other plane flying with me had it, so he just relayed my position reports for me. If one wants to go into places like Shannon, HF is mandatory since it is Shanwick Oceanic. I took a Warrior to Denmark last year, and brought a Cheyenne back from India before that. Didnt have HF for the Arabian sea, just kinda faked it
For going to Moscow, it might be possible to go east from BIRK (Reykjavik) to Norway, but HF will most definitely be needed.
I am not sure who is going to be tanking it, but have a reputable outfit tank, and inspect it. Globe Aero in Lakeland would be good for that. Because, you will be betting your life.
When I used to live and fly in Hawaii, there was a young hungry CFI who was going to take a Baron from Hilo to Cali. Lost an engine right after takeoff, crashed right back to the runway and died in a fiery crash.
If you end up doing it, you might consider when you leave for one of the oceanic legs, do it the same time as someone else, arrange a VHF freq to stay in contact with them. Maybe you can hang out in Gander, St Johns, or Goose Bay and wait on someone going across also to link up with.