The transmisson mount is removed by 4 bolts through the cross member and the two bottom bolts through the bell housing covering the universal joint. The two round circles are like rivets. Its part of a vulcinized mount. Chevs of the 40's has a picture on page 106. Its part number is 594117. The rubber on these is typicaly turned to mush and needs to be replaced. On my truck the parking break bolts in your picture have flats two flats on the thin rounded side and a typical nut on the other. I hope that helps.
