Hi there Swifty from a neighbor in Devils Lake. My advise is to go 5.9L magnum motor. That's what I put in my Duster and made stroker out of it. But even if you don't want stroker the stock 5.9L gives you better flow heads and roller cam. You can use your 340 front timing cover and all the stock 340 pulleys and such to keep it simple. If you want a stroker, Jesse Lachman in Center, ND can build you a great engine. He did my stroker. Check him out at revsearch.com.
I have a 340 torn down now from a challenger and pistons for 340 are lots costlier and less manufacturers than for 360. For 340 they want extra $$ for those parts. If I didn't have a good block I would go find a 360/5.9L.