You don't
need a lower compression ratio, but it usually helps. Basically, how much power you looking for? The D has a modest compression ration anyway (usually around 9.6:1).
Ls rods are a good start, so i'm assuming you're not looking for rediculous numbers, just more reliability. What do you plan on doing about pistons? Vitara possibly?
Changing up the valvetrain shouldn't affect compression unless you're changing out the valves that are different from stock spec, which may raise or lower your CR depending on the shape of them. I wouldn't focus on the valvetrain so much, depending on the D you're boosting. Are you working with a z6 or Y8 or other?
Oh and this should be in the turbo forum, under the high performance category
