If you have an old retainer and set of locks install a valve stem seal then slip the retainer and locks on and you can measure how much valve lift it'll handle without the retainer hitting. You need a safety factor of at least .050"...
One thing to note is that .508 cam will only have about .485~490 lift at the valve due to the complex lifter to pushrod to rocker arm angles if you are running std 1.5 ratio rockers