Gen1 (RBY) and Gen2 (GSC) stats were calculated differently. In those games, given max EVs and IVs, a level 100 Pokemon would have a non-HP stat of (2 * Base) + 98. A perfect Mew, then, would have stats of 298 across the board.
The current system (Gen3+) crippled all Pokemon stats due to the different EV method. Under this system, a level 100 Pokemon has a non-HP stat of (2 * Base) + 36 with no EVs, and (2 * Base) + 99 with 252 EVs. Then multiply by 1.1 or 0.9 depending on the nature. Since you can only put 252 EVs on two stats, this means that all Pokemon are weaker overall, but certain stats can be skewed to extremes. This is one cause of the power creep we're seeing in Pokemon: an offensive strategy only needs 252 EVs in one attack stat (ignoring the other), but a defensive strategy requires 252 EVs in both defensive stats for maximum coverage. Add in the general power creep to moves, and you've got the recipe for the current OHKO metagame we're seeing.
A Gen1 Lv100 Mew has a stat total of [2x100]+98=298 across the board, while HP is [2x100]+203=403. Easy.
A Gen4 Lv100 Mew has a stat total of [2x100]+36=236 across the board before EVs kick in. 4 EVs = +1 stat boost, so 252 EVs in a stat gives it +63 (236+63=299, nature: 299x1.1=328 maximum). If +63 is given to two stats, then +1 is given to a third. (HP is [2x100]+141=341 before EV modifiers).
Since Mew and Victini have the same base stats, that's what your stats should look like.