What should I do?

Build the 360. Yourself. Or have a reputable engine builder do it for you. As for the 360 over the 318, in my opinion, you won't be sorry. There's no replacement for displacement and the money spent to build the 318 can be better spent on the 360. And as has been said: upgrade the rear.

Here's a link to a recent discussion on here as to crate engines. Most of the horror stories you read on this are true. Unless the crate engine is coming from someone like Ray Barton, beware. (I've heard good things about the MP crate's, too, just no experience with them.)

http://www.forabodiesonly.com/mopar/showthread.php?t=75852