The GM distributor is a custom retrofit that a lot of guys do - to put older Mallory distributors or later standard SBC ones into a 49-53 flathead (like yours). The Chevy SBC base is turned down on a lathe to match a flathead and the advance mechanism is setup/modified to reduce the total mechanical advance (there are a variety of ways to do this). Contact 'Charlie NY' on this board - he does great work and may even have one on the shelf.
As others mentioned, don't bead blast on an assembled engine. Pull the heads, pull the intake and I'd probably pull the pan as well. If this engine has been sitting, then it will most likely have a bunch of sludge and crud in the pan. Might as well clean it out (and clean out the oil pump and screen). You don't want top pump all that crap through the bearings. Back in the day the non-detergent oil created a TON of sludge - you need to clean that out. Then you "purdy up" these parts while they are off and put everything back together.
If the engine has sat for a long time, you can inspect the bores, check the valves, etc.. In some cases, everything is cool - in others you may find it needs some work. You won't know until you look!
Gaskets: Buy the 'Best Gasket' line of gaskets - guys like ThirdGen Auto and Mac VanPelt on this site have all the parts you'll need.