I use only a positive type seal on heads I build. With the proper clearance, I see no problem with adding newer type seals. Mopar used a lot of the umbrella seals with no problem. Umbrella type seals are just diverters, the stem and guide opening are still exposed just as if the seal wasn't there.
If you are having smoking problems on start up, grab hold of each valve spring / valve assembly and see if you can wiggle them side to side or forward / backwards. If you feel any movement at all, the stems or guides are worn. New seals might help for a while, buts its not a cure all.
