Can you run 11.5 high lift cams on a stock block, or will it interfere with piston?

 

timing is generally more important than lift. lots more duration can cause interference but depending on the setup advancing or retarding the cams can make the interference go away.
unless its way off you usually need to just put it together and see if it fits.

 

Yes you can. You just need appropriate valve springs and retainers. Guys run the GSC S3 on the stock bottom end routinely. Those cams have 11.7mm of lift.