Allowable angle for driveshaft CV joints

Planning on a 540 Chevy with a powerglide and c5 diff and suspension. Looking for help in determining allowable diff setback to gain legroom. Apparently, 20 to 30 degrees is the maximum CV drive axles can tolerate. Any help will be welcome. If so maybe I can set the driveline back 2 to 6 inches...??
Bob Ransom
Kenosee Lake, Saskatchewan Canada
b.ransom@sasktel.net
Bob Ransom
Kenosee Lake, Saskatchewan Canada
b.ransom@sasktel.net