anyone have a .513 lift cam and stock heads?

You can always use a checker valve spring with the retainer you plan to run and measure the travel you have until the retainer touches the valve guide. If you subtract the minimum allowable clearance required between the guide and retainer at full lift from the total travel distance, this will give you the max allowable lift with your combination of parts. I would check a few valves to make sure the machining is constant. You will likely be very close to the limit. If you machine the guides now you will be able to swap to higher lift cams later without pulling the heads. I believe you can also use a better quality valve seal. Something to think about.

Use adjustable rockers to avoid the pushrod breaking the rocker. It has happened to me as well.