Now if the war were somehow delayed until the 1880s, you have something like the Maxim gun, barbed wire, and other innovations that would increase the power of the operational and tactical defensive. That would perhaps change things in favor of the South, especially as it would likely persuade them to adopt a more defensive strategy than IOTL.
Problem 1: With that is that the South's industrial base was incapable of producing
safe-to-fire cartridges for weapons like the Henry, the Spencer, and the Sharps rifles. The mind boggles at the thought of them trying to supply bullets for Maxims, assuming every single gun comes from Europe.
Problem 2: By 1868 the UK has passed the 1867 Great Reform Act, making support for the CSA far less palatable for British politicians.
Problem 3: If the ACW is pushed forward to 1868, does Nappy III still go forward with his invasion of Mexico, risking a war with the USA over a violation of the Monroe Doctrine that the British had supported since it was issued? Methinks after the disastrous first year of the French invasion, once everyone realizes what is going on and that the Mexicans are making a serious fight of it, ITTL Nappy III's little adventure will end in early 1862 with two telegrams. One from Washington; and much more importantly, the other from London.
Problem 4: How soon do affairs in Germany and the FPW cause a total distraction for the Imperial French?
Problem 5: With the fall of Napoleon III, the CSA has lost any remaining friendly and/or "interested" powers in Europe that would be even remotely willing to come to their aid.
Problem 6: The Trent Affair is butterflied
Problem 7: Russia's sale of Alaska is completed by 1867, losing the USA $67,000,000 but gaining them $$$.