Go for it.... As somebody who has driven a 25 year old Landrover from the UK to Moscow , via Belarus , and all the Baltic states i would say get on with it.....
Yes , you may break down , get lost , or suffer any other kind of problem , but what the hell , it will be an adventure...if i had the time and the money i would give it a go.....
Incidentally....during my trip to Moscow i fell in love with Poland as i passed through , and now live here....So...if you pass this way on your trip , call in , make repairs , have a beer , and camp for free......The rally will be a laugh....go for it....!