IT DOES NO GOOD TO HAVE A BIG Cam that the heads won't support.
Duration @ .050 is what you need to look at, rather than advertised duration. If it were me I'd keep that in the 230 -240 range. The more duration you have the more compression you will need. Too much camshaft duration will bleed off a lot of cylinder preasure at low rpm. Not a good thing with a street driven vehicle with low compression.
BUT....
Since it's a big block it will have torque on the botton so you will probably get away with a little more... Just my opinion...I'm no camshaft guy by any means.