340 4 speed to 440 4speed conversion

Starting to look like a real pain already.

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It's been done many many times. The standard 70-74 BB bellhousing should work. Most non OD 23 spline transmissions had the small bearing retainer.
The Z bar will need some work. Motor mounts are as easy as ordering them, or finding them in the for sale section here sometimes. Water pump housings can be found in either left or right inlet. You'll need a short fan clutch or something else that works.
For the exhaust, manifolds would be the easiest and cheapest. BB manifolds are not worth a small fortune unlike 340 manifolds. Some folks have made the Schumachers fit. Pro Parts fit for sure. TTI's might.
The hard stuff is finding traction, patience when changing plugs, and the elusive dual purpose grin remover/passenger seat $hite stain cleaner.