My 6.1 retrofit thread
Pic 3 shows the factory valve spring and cage balancing on the head -
Just in front of the removed spring and cage, you can see the combination seat and seal - this has to go as well....
Pic 4 - This is aftermarket replacement seal, locater and shim. Thanks to
Craig Thibeau from Thitek heads for the deal on the springs and locater/shim/seal kit.