helper air springs for rear coils?
 

anyone have a source for a set of helper air springs (air bags that go inside of the coils for inflation when carrying heavy loads)? JC Whitney sells them for late 60's and 70's, but not 60-66. Or at least they don't list them as fitting. Sounds like a great idea for those of us who want a halfways decent ride when just cruising around without a heavy load.