I have a 4-speed behind the 225 in my '76 Dart Swinger, and I need to change the fluid (after 225,000 miles). I've heard of people running automatic fluid in their standard trannys. What are the advantages/disadvantages? Does one protect the tranny better (this is my first car, so I'm sure I'll miss a shift or two...)? Any recomendations -or things to look out for while draning/refilling? Thanks.

Ma Mopar in the service manual, suggests using Dexron/Mercon ATF for your gear box. Many people use this as it helps make faster shifts.
Others use 30wt motor oil (I suggest non-detergented oil to save the brass synchros). I use 90wt in my A-833OD, it's a bit stiff during the winter but after a quick run down the block it gets better.

If you pop the box open and it's ATF run ATF, if it oooozes out, you're probably running oil.

Depending on your 'agility/ability' you might want to have a shop do the job, since draining is the easy part, trying to pump oil into the top plug isn't easy with the 'el-cheapo' pump under the car on jackstands....

-D.Idiot