The adapter plate you're hearing about is used to relocate the pump higher on the block, and it covers the original hole in the 235 block. It allows the earlier style pump for the 216 and splasher 235 to be installed, which does not have the impeller that extends into the block. The early pump has a rear cover plate, and the impeller is fully contained by the pump housing. The harmonic balancer swap is required because the earlier pump uses a wider belt. It will also be necessary to swap to a wider generator pulley.
Jerry

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