Willy,
Your intake manifold it is a Mustang D3ZE (without eggs shaped) not a Pantera GTS D3ZE intake manifold (with eggs shaped), so if you want to install a squarebore Holley (4150 or 4160) or Edelbrock you have several choice for the intake manifold depending on price and therefore performances, I see at least 3 for a stock engine, in ascending order:
1) Machining your intake D3ZE to have at minimum a GTS egg shaped on secondary ducts but you have to find a spacer, to limit disturbances (like mine ...?) to go with. With the Holley carburetor, the spacer must have a minimum 1/2 in thickness for the passage of the throttle bracket, I don't know for the Edelbrock one. For the maching of the eggs shaped, carry out the same machining of the primary ducts with a diameter 43.2 mm (1.7in) and apply them to the the secondaries ducts with the same diameter and the same center distance 47.7 mm (1.88 in) and the distance center between primaries and secondaries are 46.2 mm (1.82 in) to have a square bore.
2) buy an Edelbrock intake performer 4V #2665
3) buy a Blue thunder or Scott cook intake manifold for pantera
+ buy a Holley or Edelbrock 650 CFM
For information, I looked at a Holley spread bore 4165 or 4175 and you cannot install on pantera intake manifold because the center distance of the primaries ducts are bigger.