🚀 go-pugleaf

I am encountering some crashes running System 6.0.5 that I am told
may be avoided by increasing my heap size.  I do not have access to
CE softwares "HeapFixer" which solves this problem.  A recent
issue of MacWeek stated that the SUM Tools program that comes
with SUM II can also increase the heap size.
 
I own SUM II but I have been unable to determine how to increase the
heap size with it.  In SUM Tools, under the edit volume boot blocks
dialog box, there are places to enter "System Heap Size for 128k"
and "System Heap Size for 512k".  Does anyone know where to increase
the heap size for a Mac Plus, or later Macs.  I suspect in the
512k part of the dialog box is the appropraite place.  Any idaeas about
what values to put there?
 
CE's HeapFixer sounds easier than SUM to do this.  I wish CE would
sell it seperately or make it Public Domain.  Does anyone know which
CE products HeapFixer comes with?  
 
Thanks.  --Joe