You can get a nice non intercooled V3 Si-Trim
Vortech kit for about $3,500.
http://www.jegs.com/i/Vortech/933/4FA218-040L/10002/-1?parentProductId=1137093 It comes with everything you'll need for the install. The kit will utilize an FMU, so larger injectors aren't immediately needed. You can always add those later on down the road if you feel it necessary.
With a Trick Flow Top end kit and Vortech Si you could easily make your 425hp goal without pushing the limits at all. The stock HO block is limited mainly by the block itself. You're more likely to split the block before hurting the internals, so I wouldn't let that concern you.