Paul,
I modified the early Holley regulator about 12 years ago.
Quite easy once you see the principle.
I can't remember what spring I used but it was lighter than stock.
Holley has made the same regulator for some time:
http://www.summitracing.com/parts/hly-12-803bp
Note that they don't make a 12-804BP, which would suit what you need.