Here is a PCA plot including an ancient Slavic sample (Rus.Slav) from the 11th century in Russia. He clusters with west Russians coming closer to Poles and Ukrainians showing that indeed certain slavic populations drift towards balts. He may have also been already admixed, that is yet to be determined.
Whats interesting is that the PCA also contains a half belarusian/hald Denmark (half.belo). He is literally almost Identical to me on this PCA. There is also a sample(half.russian) whihc is half russian and half american. The Moravian(czech sample) on the PCA is clearly more eastern than both of them.