Exeter,

I'm in a similar process designing floats for an older
trainer..and locating the CG and the balancing act thing.

I ran across this site: http://www.rrcc.org/downloads.htm

Down the page is a program by Mike Sayer,
called Model Aircraft Weight and Balance

And then I found this one which has helped me
the most, because it is simple: http://www.seniorpattern.com/pdf/BalancingAct.pdf

Hope this helps you.
Good luck, fly high be safe, later, bud