I'm pretty sure they used the unmbrella type seals. I asked the salsman who sold me the rebuild and he said they did not use the GM o-ring seals, but were a step-up with the umbrella style. On a side note, I bought an '86 GMC with a 305 from my neighbor. It was puffing blue smoke too at start up. He too, had changed his oil religiously and was disappointed like I was. He had used 10W-40 oil. I switched that engine to 5W-30 and it quit smoking completely. I am thinking that "thinner" oil runs off the valve stem better at shutdown and isn't around during start up to be a problem. Does that make any sense? Oil viscosity always confuses me...
