Without machining the valve guides down in height, as well as reducing the od of the guide, and going to PC type seals, machining the spring pockets ( depending on the cam profile and springs required ) and pinning the rocker studs ( or drilling and tapping for screw in studs ) the absolute most lift you could run would be .470 before the retainer contacts the top of the guide.
To get the full advantage of the camshaft you will need to have it tuned. The stock computer has a 5200 rpm limiter from what I have read, so most people obtain a newer 0411 computer, which is more supported as well as having a faster processor, and the ability to run E fans.
Long tube headers will help out in the torque department. The stock internal injector fuel system will only support so much power. From what I have read it flows enough fuel to support 400 hp at it's limit. ( I have not done the calculations )
To recap: to be optimized for a moderate camshaft figure on spending $1000 or so. If you want more than .500 lift it could triple that amount of money as the most cost effective move is to ditch the stock heads in favor of aftermarket ones that allow more lift. Then you run into limitations of the fuel system.
Before spending any money on an engine it would be wise to do a compression check at the very least. If the engine has high mileage it may be more cost effective to replace it.
