That is a positive type seal, although the valve stems are set up w/the same double grooves (one for the keepers, the other lower groove for the small O-ring type seal) and there is a tin oil deflector, like has has been used since day one, pretty much.
I don't have a part number, but the seals will be the same as those used on a 1987 Camaro 305 w/TPI, for example. Some sources cite the GM factory positive seals as fitting a 0.561" SBC guide boss. Measure the guide boss OD to compare, most aftermarket type positive seals have a smaller OD (=/< 0.0530") to allow an aftermarket/double spring to fit over them. You should be able to find the seals at any parts store, just inspect them first for having similar dimensions as the ones you have.
BTW, that is an exhaust valve (you will note the spring retainer is also a valve rotator, found only on exhaust valves). The order is (from here
front | E - I - I - E - E - I - I - E | rear