Thanks to my favorite chassis cleaning product, aptly named "Super Clean", I was able to get the chassis looking respectable in less than an hour.
I saw someone recommend this stuff, available at AutoZone, on one of the old-radio forums, and it works better for removing old nicotine residue than anything else I've tried - literally, spray it on and wipe it off. Awesome stuff!
Here's what it looks like after a quick spritz and wipe. Amazing!
The finished product: Came out pretty nice, little corrosion toward the rear, but much better than before.
Under the chassis, I cleaned-up the wiring around the modified mixer stage (more on this later), replaced the few tubular paper caps and the mica wafer inside of Z2 (dreaded silver migration disease).
Above is a shot of the underside of the mixer after all cleaning-up all of the flying leads. Unfortunately, that all may have to go! When I started alignment, I found that, no matter what, I can't get the dial to track properly across any of the bands, and this seems to be due to interaction between the RF and LO inputs of the mixer - there's not enough isolation, and the alignment of the RF side is affecting the LO frequency - probably why the AM band was inop. So, unless I can correct this, I may remove the Pullen circuit and put everything back to it's original spec.
Now, for the archeology part: I forgot to take a picture while I had the front panel off, but penciled onto the chassis behind the panel is the callsign of, presumably, one of the previous owners: W8NYI. I looked through back editions of the Callbook (scans are at archive.org) and found that W8NYI was Richard Smith, who lived on Prairie Street in Detroit - which was surprising, because I live in the Detroit area and purchased the rig in Eastern Ohio... So, the rig has come back home!
Unfortunately, the last Callbook in which W8NYI appears is 1975, so it's quite possible that he became a silent key. Since the 6DJ8 tube used in the mixer dates the modification to the late 60s/early 70s, I envison OM Richard toiling over it in the shack of his QTH in the old house (now gone) on Prairie Street. This is why I'm reluctant to remove the modification - It's part of the rig's history and W8NYI's legacy; I sure hope I'm able to get it to work!