IMO, at this point it's not whatever the original bike is, so completely ignore the price of a CB550/CB750 in stock form. This does look rather middling -- decent frame chop job, tank looks janky (possibly home spray bomb?), probably much else not seen.
That's not to say it's not a good bike, but it's just another late 70's early 80's runabout bike, not worth much intrinsically, just comes down to if you love the look, maybe it's worthwhile, that's up to you though.
That '78 posted is a remarkable deal though, go for that one.