If my opponent flips heads for Shuppet's "Enveloping Shadow" attack, can I still play Antique Dome Fossil or Antique Helix Fossil since they say to "Play this card as if it were a 60-HP Basic {*} Pokemon"?
No you cannot, because it is still considered to be an Item Card while in your hand.
Source: TPCi Rules Team (2024-09-26)

Relevant cards

Note: All applicable cards may not be listed below.
SV1_87
SV1_87
SV35_152
SV35_152
SV35_153
SV35_153