360 magnum into '66 Valiant

And another heads up- depending on what you're using for exhaust. If you're running headers, you'll have to grind the mid-block "Magnum" mount bosses down in order to clear the headers. The headers may also need to be modified to clear the 727 at the bellhousing, since it is wider than the 904 that came in these cars.
If using LA manifolds, you may need to run double exhaust gaskets on the driver's side, in order for the manifold's downleg to properly clear the Magnum head. In some extreme cases you may need to run a header flange between the head and manifold as a spacer.
The transmission crossmember also needs to be modified in order to run dual exhaust.
Dual Exhaust Crossmember Modification on 64-66 A-Bodies? | For A Bodies Only Mopar Forum