I added a line like this
  options         NMBCLUSTERS=1024
to my CONFIG file, ran config, make depend, and make.

It didn't build a new param.o.

As far as I can tell from greping the sources, the only place 
where NMBCLUSTERS gets used is the following line in param.c:
  int     nmbclusters = NMBCLUSTERS;

Did I miss something in the new-kernel recipe that covers this case? 

What should I have done?