Very interesting! The M-frigates were definitely a case of "capability creep". I have a Dutch-language book on the history of the M-frigates at home (I'm sure you are aware of this book?). Let me look at it tonight and see if there is anything useful in there for you...
a book? if you have any intel on these ships, please share it, because I don't have much information........ only drawings, length, displacement and a bit about weapons and radars is known to me. for the rest I have to guess mostly, so if you could scan some stuff....
and for the goalkeeper: it was first delivered in 1980. so in 1977 they could of course plan to have them on new ships.