Alvin:
You need to first see what the temp of the water is. From there how much differance between air temp and intercooler water temp. I'm thinking that it is not far from each other. But if it is way off then, yes a bigger intercooler should help. You then could have a chip burned with a lot more timing in it.
Ruslow:
The biggest reason that the L does not come with 4v, is that it does not fit under a factory hood. I think someone said it's like a 1.5-2 inch taller.
My thinking is to have the stock head ported, increase the valve size. This would be much less money and done right should bring a 35-50hp gain. With a good blower grind cam, 50-75hp total gain. This with other little mods would put you around the 475- 500hp mark. I don't know the limit on the bottom end, but would not want to go any higher than this on stock powdered rods.