Well, pulling out the silver/mica capacitor thingie did the trick. The ski-matic
shows that the AM cans are 100mfd capped and the FMs are 33mfd, so I'll just get standard ceramics and solder them in.
I guess this was a way Motorola was going to cut costs and keep quality, but it didn't pan out over 50 years, though let's be honest - the thing wasn't expected to last that long. It's a neat design that looks like it could have been easily automated, and the cans themselves are pretty darn solid. Except for those darn caps. Oh well.