Gen 3 early vs newer design

[MitchPower]

In the valvetrain articles in the section 3x00 performance it says that the Gen 3 valve guide changed in late 99 and that it won't accept LS1 spring seat, my engine is a 3400 from a 99 venture, how do I know wich design is mine and for LS6 spring do I need to get the LS1 spring seat or if the LS6 spring seat have to be used with those springs

[SappySE107]

ls1 and ls6 springs are the same as far as size goes. What color are you valve stem seals? If they are orange, then they will fit the LS1 seats no problem. Otherwise you have to machine the guide or the spring seats.

[Superdave]

it takes like 30 sec to hone out the LS1 shims to fit the larger guides..