The stamp for ID should be on a pad next to the distributer hole. For parts, I prefer Federal-Mogul (Fel-Pro, Sealed Power, TRW, Melling) available at any good parts store. If they don't have them (or don't want to deal with an old engine) Patrick's and Langdons can hel you out on parts, too.
On the second question, don't sandblast the block!! You'll most likely never get the sand out of it. Take the block and head to the local machine shop. They'll hot tank it, which will remove not only any acumulated crud, but the old paint and rust as well. They'll also mic it and recommend any machinig nesessary, such as boring and any crank work, plus re-babbiting if needed and install the cam bushings. You can also have hardened seats for the valves installed at the same time.
For paint, you'll want to use hi-temp paint speciicly for engines. Seems that the paint from the Filling Station is popular here for best match to the original color. As to whan to paint the block, I did mine before assembly, masking off any holes and gasket areas.
