Used heads are all over the place. I have seen them from $400 up. A new head is over $2300, and does not come fully machined!

All you need to measure piston crown rise above bore is a vernier/dial caliper with foot attachment. You could also use a linear dial indicator and stand. You could even get away with a precise steel rule, but that will be a judgement call.

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Chief

1991 350SD