I am a very casual follower and cantflip has a lot more to offer (don't you love this place?). I would take his advice on the rust.
But I still think this is a sweet roller and of course you HAD to buy it!
I feel ya bro!
If I were in your shoes and I think you've made up your mind...just get it running and move it on to somebody who dreams of a B-body like this.
Drop in a 440? OK...whatever.... If you want to race it yes.
For the street, many came with a nice 400 4bbl/dual exhaust combo. Even a good used 340 or 360 would do it some justice. ("No" on the 318, IMHO.)
To quote Wikipedia:
"Total sales this year were around 108,000 units, the highest ever for the 1971-74 Charger generation, though more than 60 percent of the cars had the non-high performance engines. "
Yea, I know probably seems like waste of a good race chassis, but I think you would score more $ selling to somebody who "dreams" of racing rather than actually does it.
Spend the money on getting it nice and cozy inside. It's already in good shape, as you said.
The purple paint? Yeah.....not everybody's cup of tea, but fits this era just right IMHO.