fortran - changing precision of real numbers

[Dima Sorkin]

Hi.
 I have a code written in single-precision (MIEV0.f by Wiscombe).
I want to compile and run it in double-precision.

Is there some compiler options in gfortran ?
(in g77 ?   (if I will have to use old computer))

In case the answer is 'no', is the following sufficient:
1) change 'REAL' type to 'DOUBLE PRECISION' globally in the code.
2) change all calls to 'REAL(..)' function by 'DBLE(..)'.

Thank you.
Regards,
  Dima.