You can use the heads with o-rings, they make it harder to blow a headgasket. But look at it this way, if something goes wrong, a headgasket is easier to replace than piston rings.
IIRC, the 1.6" springs are the dual spring setup, and can handle .600" of lift. You're gonna want the duel spring setup with that cam, not the single spring. Although the single spring is rated for .540" lift, it's better to have stiffer springs than absolutely neccessary to avoid valve float at high rpms.
It's a good idea to replace the lifters while you're in their, just for insurance, although it's not absolutely neccessary.
The valve springs come already installed on the heads.
I would suggest switching to some stud mount rockers, otherwise IIRC you'll need to buy a kit to convert those heads to accept your stock pedestal mount rockers (I think Cobra's are pedestal's right?). Either way, buy some new rockers, the stock ones are junk.
As for what else you'll need, you'll need bigger injectors, a bigger maf (calibrated for those injectors, unless you're gonna tune around that), a bigger fuel pump, and a variety of tools, like a torque wrench, feeler gauge, timing light, balancer puller, etc. etc.
