If it was mine i would find a 2.3 16 valve scorpio granada and fit that complete engine in the sierra.

Porting the intake and a bigger thottle body will not give any usefull power increase imo.

Throttle bodies on a custom intake with a custom tubular manifold on a aftermarket ecu will give greater gains but will be expensive.

With the right parts from the fords parts bins anything is possible.
16 valve head from a galaxy? RS 2000 cams? Or the easy scorpio option.

The choice is yours.
Tidy looking saff is a rare find these days.