Depends on how you are going to use the van. Will you be hauling a full one-ton load? Will you be building a heavy custom interior? Will you be pulling a heavy trailer and hauling a heavy load? If you answer yes to any of these, I would recommend the 727.

However, if the van will only be used to haul light loads, will have a lightweight interior, or only be used for cruising, then I would recommend a 904T out of a post-1980 truck or van.

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Casually looking for a Clifford hyperpak intake for cheap.

Be aware of the crankshaft pilot hole diameter change in 67 or 68. The Cortezes used manual transmissions, but you are asking about installing an automatic transmission. The size of the pilot hole on the back of the crank changed sizes and post-68 torque converters won't fit in the pre 68 crankshaft.

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Casually looking for a Clifford hyperpak intake for cheap.