Certainly the Japanese military was much weaker then--much of the navy that went to war with Russia OTL was purchased with the money they received in reperations from China. So the IJN will be considerably smaller. The Army, too, come to that--it was expanding rapidly at this point.
I do wonder how easy it will be for the Russians to project force that far, though. The navy barely made it in 1905. I have to imagine it'll be even harder here, given slightly worse tech, and perhaps less well-developed French coaling stations. The Russian army is in even worse shape. The TSR has just started. It's still over a decade away from completion. The Russians will have a devil of a time sending troops to the Far East, and keeping them supplied will be even harder. Probably the best the Russians can do is send a punitive expedition.
The big question I have is this: what are they fighting over? The assassination is a good casus belli, but at this point what are the Russians and the Japanese competiting over?
The 1882 and 1884 revolts in Korea that both resulted in stronger Chinese control over Korea. At this point, Korea was somewhere between a vassal and a colony of China. The "race for concessions" between Russia and Japan (and to a lesser extend, the French, British, and Americans) is still in the future. So the main point of contention between Russia and Japan in 1904 is not around yet. The Russian troop presence in Manchuria, another point of contention with the Japanese, won't happen until after the Boxer Rebellion in 1900.
So, really, what are they fighting about? At this point, Russia has no reason to expect that defeating Japan would lead to a better position in either China or Korea. They can probably sink the Japanese navy, but Japan is already strong enough to prevent outright conquest or colonization. They can capture the Kurils, they can punish Japan. But is that enough? Does it justify the expense of sending the fleet halfway around the world?
Still, if they do it (and they might, just for national pride and honor) it will probably set Japan back for a generation. Without the Sino-Japanese War revealing Chinese weakness, China might be able to hobble on for a while longer. Maybe Russia is the one to take over control of Manchuria and Korea. Maybe Germany still sets off the Far Eastern Question in 1897, regardless of (presumed) greater Chinese strength. It changes everything.