k frame difference?

just wondering, but I am always searching for a v8 k frame for my 73 duster and I always see them for sell but they always show up to 72. Is a k frame that is pre 73 not compatable with my car?
On a related note, if You're switching out a slanty, there may be members interested in a spool mount k-frame for their '72 and down slanty equipped rides.....post in
the mech. parts or suspension etc. for sale forums here.................