Packages do exist, horsepower depends on the cam, but what ever route you go with the DOHC Modular motor the cam packages are gonna be expensive $$ 1500 range for just the cams. Like I say, the horsepower that the cams will use depends on what combo you go with.
Yup from what I have been told that are heads have hell of alot of power to be tapped out of them, if you have the money. These DOHC heads are not cheap to build up. Been looking into building my heads up and lets just say for parts and labor on the heads (not including removing and installing the heads off the car, I will do that myself) I would almost be able to buy a supercharger.
The amount of power you get from h/c will depend on your current mods also. They make regrinds for as low as $500(core required) so there not totally out of my price range. Comp cams just started making cams and valve springs for the DOHC I haven't seen any prices yet though.
FR500 valvtrain (new billet cams, lightweight race valves, high lift springs, retainers) is like 1200-1300 bux...i think by far the best deal out there right now....
for the heads....just have to find someone w/ experience porting 4v heads...there are guys out there that know their sheet....