He was only superficially close to South West Slavs to be fair. He was also of low quality. As such, he's likely not basal M458*. Due to the quality he couldn't be placed further. Wouldn't be surprised if he was also L1029 like the late la tene Czechia sample.
I don't think there can be any doubt that M458 existed near to or overlapped with the Balto-Slavic territories. So my guess is Southern ir southeastern Poland. Most M458 diversity in Belarus is linked to Poland and its heavily concentrated on the South West border.
There's even more diversity in part of Russia. Whether that's linked to Polish migrants is another story. Amd by Polish I just mean from Poland the territory and not nationalistically speaking. Even the new Southern Poland samples were super diverse in their M458 clades which dominated.
While a low sample size, Slovakia and Belarus have the same number of M458 on ftdna out if 50. Only one Belarusian belongs to M458*, compared to 10 times that number in Slovakia.
Germany, Poland and Russia currently have the most. In that order.