over 40 had the obvious solution (look at the balancer) I assumed that you had no timing marks on it. His answer would be my first suggestion if your balancer has marks on it (I can't think of why it would not). If you dont have marks, you can use my idea with no special tools, just use a bolt of the right size for the piston stop.
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67 Fastback - Arctic White Pearl paint
351W ,Trick Flow Aluminum Heads, Edelbrock TorkerII, Comp. Cam, Performance Automatic C-4 Trans, 3.55 gears, Front Disc Brakes, 1-1/8" Fr. 3/4" rear sway bars.
My 351W Fastback
