Overdrive Options
If you're just looking for "a number" for the 2004r swap, here is a reasonable breakdown of what it will cost. This is going from my own personal experience with what I did to get a 2004r in my car.
Trans - I did a ton of research before buying my trans, and this is who I wound up going with. This guy is well known in the Grand National world for his 2004r's. I spent quite a bit of time on the phone with Lonnie and the Stage 1 trans is what he recommended, but I chose Stage 2 for room to grow.
http://extremeautomatics.com/transmissions/2004r.html
Adapter - I went with Wilcap for the adapter, and it's a really nice kit but pretty expensive. Since you're running a 318 it would be $575, but for those reading this, it's an additional $100 to balance the flexplate for a 360. The only thing I had to modify was when the mopar starter hit the bellhousing, so it just needed a little trim. The TCI kit is cheaper, but you have to cut the adapter plate.
Wilcap:
[ame]http://wilcap.com/318350.PDF[/ame]
TCI:
http://www.tciauto.com/tc/318-360-chrysler-to-chevy-transmission-adapter-kit-6-hole.html
Converter - This is one of those questions that you'll get 10 different answers by asking 10 different people. There are several good companies to choose from for a converter, but this is what I chose due to them being a vendor with a good rep on another site I visit.
http://www.revmaxconverters.com/index.php/torque-converters/car-torque-converters/2004r.html
You'll also need the TV cable setup. Without knowing what sort of throttle/kickdown bracket you're using I can't tell you exactly what you need, but for sure you need the geometry correction plate for your Edelbrock carb.
http://www.summitracing.com/parts/TCI-376710/
Now add the cost for the TV cable and bracketry (~$50), a driveshaft (~350), DEX VI trans fluid (~$80), and $100 for misc materials to build a crossmember and whatever else it takes to get it installed.
I didn't add it up but that's roughly $3,000 to make the swap. Compare that to a Gear Vendors unit for $2800 it seems like a wash, but unless you've already got a built trans and a good converter the 2004r swap still comes out ahead imo. Not to mention the ability to lock the converter while going down the highway.
Just some stuff to think about.