Choosing the best 5.7 engine and Transmission

Do the math, the new hemis are cool and all but expensive...

You already have the trans if you stick with older iron, and will save a ton of money by doing so.
You could keep your 318 and stroke it, or just check out rusty's hot rod bliss thread.
RustyRatRod's Guide To Hot Rod Bliss

or,

Magnumswap.com - Your source for Dodge Magnum and Mopar engine swap tech.

or,

have you considered something like this?

Mopar 360 engine and radiator for sale

or,

have you considered talking to @Johnny Mac from blueprint engines?