schumacher has the motor swap mounts
Exclusive mounting brackets for your '63-66 Dodge or Plymouth A-Body; bolt a 273/318 or 340/360 directly to your Slant 6 or V8 K-member with no cutting, welding, suspension changes, or K-member removal. Available as 273/318 replacement or Slant 6/273/318 to 340/360 upgrades. Kit includes...
www.engine-swaps.com
everything else "fits" but...
you'll need headers-- TTI or doug's (i know TTI fit with power steering, not sure on doug's)
you'll need the factory 90° oil filter adapter-- and
specifically you'll need the 64~66 unit that is a true 90 not the later one that's at a lesser degree and will hit the frame. OR a remote mount filter.
you'll need a different radiator. if you upgrade your brakes (if you haven't already) you'll need a combo/metering block that doesn't poke out from the frame too far or it'll sit too close to the exhaust.
a 904 can be built to withstand the abuse it'll take behind a 408, but a 727 would be the better choice. it'll be a tight fit and there will be some body massaging-- namely the pinch weld.
you'll need the V8 center link to clear the oil pan. so be ready to hunt one of those down to pay out the nose for it.
and as Jim said you'll need to beat the firewall back to clear the distributor