When Did Ford change the balance on small block Ford engines?

I am helping a friend of mine change the motor in his 4x4 truck. We were wondering when Ford went from the 28oz balance to the 50oz? We are trying to determine flywheel interchangeability before we install the engine. We wre thinking 82 but aren't quite for sure.

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Ron Meyer
67 Mustang coupe (289,Windsor jr heads,4spd,3.55 posi rear)
86 Mustang SVO (Turbo 4cyl., 5spd)

<font size=-1>[ This Message was edited by: RonMeyer on 3/10/03 2:05am ]</font>

I have heard both 81 and 82. Look way back in some of my old posts. It was discussed last fall, I think.
[addsig]