If you buy a custom cam, you will be far, far ahead. On 340 inches I run 255 at .050 on a 105 LSA installed at 105 and I get almost 10 inches of vacuum at an 800 RPM idle.
I would try and get all the power you can and opening the LSA for no reason other than to try and get idle vacuum up isn't one of them. You should be able to do that without compromising cam timing.
