I then feed the generated sweep signal into the primary of the IF stage, and pick up the secondary using the y channel of the same scope. So what you see here is the response over frequency of the IF filter. Looks absolutely perfect

And while this method is great for seeing the shape of the filter response, it tells you nothing about the actual frequencies. You have no markers, unlike with a purpose build sweep generator like the Wavetek I showed before. Unfortunately, that one is of no use for AM radios, since it covers a frequency range of around 5 Mhz to 500 MHz.

And increasing the sweep frequency

This is how I spend my Friday evenings

The IFs were both off frequency. I tried to adjust them, only to find out, they cannot be adjusted. Where I thought a core slug was lurking was in fact nothing but a concrete like ferrite material. In my attempts to turn what I thought was wax covered slugs, I ended up killing one of the IF coils. Fixed it again.

And then I experimented with tuning them with additional trim caps.

These IF cans were meant to be a set and forget kind of deal, with a frequency set during my manufacturing. Somehow the frequency has drifted, by quite a lot. One of them was at 425 kHz.

Receiving some Bangladeshi(?) station. Around 1420 - 1435 kHz. (LO is at 1899 but I forgot my IF frequency, I've changed it again)
I'm located in Europe.
Ran Shazam on one of the songs and it gave me a Bangladeshi singer.

Edit: measured the IF to (469.6 +- 0.3) kHz, by injecting a signal into the mixer and adjusting for lowest beat frequency

The antenna I used: a small ferrite antenna just dangling about