Hey Jedi welcome to ford motor forum. The 289/302 pistons are the same. Stock bore both 4". The differences between the two would be connecting rod length- 302: 5.09" (289: 5.155"), crankshaft stroke- 302: 3" (289: 2.87"). If you were to use a 302 rod you would also need a 302 crank.

With good quality rod bolts your stockers will survive 6k.

Allan

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