IF dumping the /6 is what your going to do, then IMO, staying with a MoPar engine is what you should do for a few very good reasons.
Easy, cheap to get and a snap to install. For a V8 swap, you'll need to shorten the driveshaft, and get the swap mounts, which are a little pricey, but very good. A V8 radiator is recommended. I did the swap myself in a 74 duster from a /6 to 318. See here;
http://www.forabodiesonly.com/mopar/showthread.php?t=10508
As far as a cost perspective, Chevy guys pay the cheapest prices period. Everyone else pays more. Headers, heads, intakes are where we get beat. However, there design and operation is better than the Chevy engines.
IF the Chevy heads/valve train is so good, then why are the serious power makers/searchers switching there valve angles around to 15*'s from the 23* and adding a shaft for strength? MoPar gives it to you stock.
Ever notice the engine shoot outs the Mags have? Ever notice the smaller cubic inch engine wins every time?
Did ya notice it is a MoPar engine?
Look at the build specs. Make more power with less.
This applies to the big block or the small block.
IMO, I would use a 360 (There cheap in the J-yards) for the extra stroke in the crank is good for the street. More torque. If you run a big block, a 440 is a natural choice. A trick is a 400 with a stroker kit in it.
Take a peak at the racers forum and look up top for the sticky's. There are threads on what a few fella's have in there engine/car set up to run 12's, 11's, 10's, etc....