You don't need a bunch of fancy stuff for a quick 1970 Duster. You have the widest wheel wells already. Torsion bars are great, you could not give me a spring front end. Handling is quite acceptable with the 340 Duster formula, .875 torsion bars, heavy duty leafs in the back and a .875 OD front sway bar. Have your steering box rebuilt by someone good, Firm Feel does great work. The K frame is fine, all you need is a set of motor adapter brackets and with a little work they will drop right in. Swap to disk brakes and a rear, if you have an 7 1/4. A 727 is a great trans, a 904 will do if upgraded. Any Mopar engine can be made to run. Welcome, by the way.