Father-Son 1974 Duster Project

My 14 year old son just bought an unmolested 73 duster with a slant six. It is our goal to restore the car, but swap the slant six for a 318 using the Schumaker (sp) motor mount kit.
When I was a kid I had a 69 Barracuda that had a 318 with a 904 trans and drum brakes all around from the factory. I put a cam, intake, headers and 4bbl on the 318 and I drove the daylights out of that car for years without busting the rear, trans or tearing up the brakes.
This Duster has drums all around and other than the typical rusty lower quaters and floors it is all there right down to the window cranks and radio knobs.
I have read so much conflicting information here about swaping motors and what transmissions will work or not.
Please remember the goal here is to build a car that the boy can enjoy taking down to cruise night, not to the drag strip.
Any guidance from you all will be welcome help.
Thanks!