You can deburr the casting flash using a die grinder/sanding rolls. I never did this nor even thought about doing it in the past. I did do it on my 455 block because I read it can prevent any casting flash to break off and fall into the engine and smoothing the edges out can help to prevent any stress cracks as well as help with oil return.That's what I'm thinking
With the millions of engines Pontiac cast, when was the last time you hard of one going south because the casting flash broke off and damaged the engine? So it is one of those things I feel can help to make you sleep better at night, but may not make a difference one way or the other - and makes for good conversation in a group of motorheads that you deburred the lifter valley of casting flash and it cut 1/2 second off your 1/4 mile times.