Note that you can get a free plusFORT licence for use in updating public domain codes such as these. plusFORT can do the sort of spaghetti unscrambling described above but can also perform other modernisations, such as adding declarations to allow use of IMPLICIT NONE, converting declarations to Fortran 95 style and adding intents for dummy arguments. It also analyses call structures and data usage and produces reports which help modularize the code.
I’d also be happy to spend some time working on this myself. Although I’ve used a few of these packages in the past, I’m not a current user. If anyone can suggest somewhere to start, I’ll take a look.
You can request a licence using the contact form at www.fortran.uk, but because I will be completely off-grid next week, you won’t currently get a prompt reply. In the short term, please refer to the following post to get a free time-limited licence for plusFORT.