That won't work. The whole point of the 40 hp rather than a straight forward 252/252 set is to allow Weavile to switch into a non nasty plot boosted or choice scarf variant Azelf's flamethrower. If you give it the extra 1 speed and take away the hp, then Azelf can OHKO Weavile, in which case you might as well use a 252/252 set which is what I use and I must say it works great.
Well of course this set will only work if another Pokemon has Rain Dance BUt if you do have Rain Dance support then this could possibly work:
Ludicolo @ Choice Specs
252 HP/252 sp. atk/4 sp. def
Modest
Swift Swim
-Hydro Pump
-Energy Ball/Grass knot
-Ice Beam
-Focus Blast/Hidden Power [Electric]
Ok hear me out before you run in shouting how much of a novelty this is. With Rain Dance Support, Ludicolo would actually make a pretty good surprise special sweeper. a 90 special attack, while no superb isn't anything to laugh at either. Even with no speed investment, Ludicolo, backed by Rain will out run anything up to and including a Jolly Jolteon. Water and Grass have superb type coverage plus water gets a rain dance boost and Ice beam is there for type coverage, whether you want Energy Ball or Grass knot is up to you and the last slot is really a filler and Focus Blast is there for the type coverage and Hidden Power [Electric] is for Gyarados.