Definitely gonna be a shock to the system but is it really that dire? Populist Republican
"fusion politics" that put Black Americans in positions of authority alongside Whites was popular in places like Charleston post-war until the KKK literally had to engage in a campaign of extreme terrorism to break its back.
Fusion politics or a TTL equivalent probably becomes very popular post-war here, considering its appeal to both poorer Whites and Black Americans with a populist message. OTL sections of the Republican Party were not only fine with, but optimistic about black lawmakers - here the radicals will have even more power, allowing for correspondingly more audacious gains for Black representation.
Anyways, I think we haven't yet discussed one of the most major reasons that Reconstruction failed in our TL: the Supreme Court. Racists on the bench did a lot to undermine and whittle down the ability of the Fourteenth Amendment to serve its intended purpose, specifically in the Slaughterhouse Cases, US v Cruikshank, the utter disaster that was the Civil Rights Cases of 1883...by the time the disgusting travesty of Plessy v Ferguson came around, the court had already gutted any hope of federally defending the freedmen's civil rights. As the first two examples were both 5-4 decisions, changing a few seats or even one seat on the court could stop this sad miscarriage of justice before it starts.