The GM OEM part number is 3835392 which was used for both intake and exhaust from mid-47 to 54. It shows as the intake only part number through at least '57:
1929-57 Chevrolet Parts Master
There is a full set on ebay:
GM 3835392

In '55 GM introduced some new retainers including a 'rotating' piece for the exhausts - which I have seen only in aftermarket form by Thompson, Wohlert among others - and predating the GM part.

The rotation apparently helps to prevent/discourage valve seat erosion which is caused by microscopic welding of the the valve to the seat under extreme heat. This problem was most apparent in heavy truck applications under load.