(provides limited administrative exception to ability of IRS to examine Form 706 in connection with certain protective claims for refunds that are timely filed; if claim for refund ripens and becomes ready for consideration after expiration of period of limitations on assessment in I.R.C. Sec. 6501, IRS will limit review of Form 706 to evidence relating to deduction under I.R.C. Sec. 2053 that was the subject of the protective claim).