Hello you wonder if can use the new umbrella valve seals on a 78 305ci Chevy instead of old small rubber ones?

Yes, you can use the new umbrella valve seals on a 1978 305ci Chevy instead of the old small rubber ones. The umbrella valve seals are an updated design that provides better sealing and reduced oil consumption. They are also more durable and can withstand higher temperatures than the old rubber seals. To install the umbrella valve seals, you will need to remove the valve covers and rocker arms. Then, you can use a seal puller to remove the old seals. Be careful not to damage the valve stems or the valve guides when removing the old seals. Once the old seals are removed, you can install the new umbrella seals by hand. Make sure that the seals are seated properly and that the retainer clips are in place. Finally, you can reinstall the rocker arms and valve covers.