73 Project help?
One of the best things you can do right now is wear out the search function on this forum and read till your eyes bleed!Information and research is king when it some to planning for a "project".In my neck of the woods /6 cars are usually less beat down(decent body/interior/mechanicals.bought one 8 years ago for $50 and very clean) then their V8 brethern,but that would leave you looking for a V8 K-member or using "swap" mounts from schumacher etc(added expense)unless you use elephant ears.
a-904 trans will come with the 318, and is a good trans.
Mild 318(cam,headers,4bbl,etc) an 8 1/4 will work for awhile till you move up the power scale then want an 8 3/4.