According to my 74 parts manual, the 1970 the 10 bolt cover axle housing used in the 40 series, (yours), should use part number 1234624. Your car should have the first of the "Corporate 10 bolts". These can be identified from the BOP 10 bolts by having a round diff cover, not having the cover with the indented sides.
Buick Master Parts book from 1970 shows the bearing w/retainer part no is 7451895. The 1972 edition shows it updated to 7451959. Pictures of some 7451959 boxes on eBay show the bearing industry number of NDH U1578ZJJRA. A GM supercedure book shows a still later no of 9428059. These are all for the 10-bolt
rear axle cover design. This is a type "B" rear axle.
The seal shows up in the Buick Master Parts book as no 1234498. A GM supercedure caralog shows it changed to 1255938 about 1/82.
Www.rockauto.com shows they carry a Timken seal no 712146 that is the same as the Buick nos. It doesn't turn up by searching Buick applications. Their site seems to revert to the 12-bolt Chevy type "C" clip-in axle types or a Pontiac type.