My 1966 Dodge Coronet

The problem you have with 68? and earlier autos is that the converter snout and crankshaft converter pilot hole is smaller. There used to be a bushing you can buy, but I do not know if or who. It is just a ring, you could get one machined if you have a friend with a lathe

The other thing is, the 5.9 Magnum is externally balanced "weighted" but it is DIFFERENT than a 360LA. The LA engines had weights welded to the converter, which was keyed by the offset bolt. The Magnums are externally weighted on the flywheel/ flex plate and the converter is "neutral" and so will fit in any position. So you will need a matching weighted flex plate. If the converter is not too large, you may be able to use the Magnum flex.

You will also need to do something about a pan. Not sure what sumps fit a B