J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment backstay

1. To the best of my knowledge the backstay lends no structural support to a 7/8's fractional rig with swept back spreaders albeit for inducing mast bend for main sail trim.

Mostly true - it does prevent the mast from rotating forward with forces from the headsail and spinnaker.

2. Is approx. 6" mast bend with the backstay adjuster all the way down normal?

That sounds about right

3. Are modifcations to the backstay adjuster subject to class rules ie. replacing the 3/16" stainless with amsteel and replacing blocks?

You can't replace it with Amsteel under class rules. You can use whatever purchase system you want with the "pincher" on the backstay. Hydraulic cylinders are not legal, nor are direct connected purchase adjustments to shorten the backstay.