If you bead blast, wire brush or scrape the inside metal parts - PAINT THEM, but don't tell anyone. The metal interior is 50 years old and probably very rusty. Removal of rust also takes away a surface material called the "patina". Moisture will enter thru the cowl in normal operations and really rust everything away if it unprotected. Do not use primer, moisture will penetrate primer. As for the exterior, I use a semi-gloss clear (Eastwood Diamond Spray) very lightly. The brackets are semi-gloss black but clean the rivets and mask with 5/16-3/8 "dots" made from masking tape.
Check out the Library, 64-66 section, for a detailed motor how-to.
Jim