[Eliot Ness]

Yikes, that is a tight chassis!  As for resistors I'd say over 20 or 30%, but if they're hard to get to and not in the SW area I'd probably leave them be unless they are more than 30%, especially since your AM is working good.

Sounds like you have a good signal generator.  How far apart on the dial do these frequencies duplicate themselves? 

I'd pay particular attention for an open antenna coil or other problem in the SW circuit..... there are a lot of contacts for band switching.... I'd make sure all of those were clean and making good contact.

Good Luck!