According to a 1987 General Motors Performance Parts catalog I have: ID # 3947886 is part # 3959105 Piston assembly STD, 427 CID, Chevrolet 68-69 W/H.D. & Aluminum Block (RPO L-88 & ZL-1) 12.5:1 Open Chamber, Forged Aluminum, Floating Pin Design, Use retainer P/N 3942423 (I.D.3947886 or 3959108) I hope this helps.
Bill
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