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Here's a nice description of a simple AM detector:
? ??

I'd first try attaching the diode (1n34a, or perhaps a BAT54s) off of pin 2 of T5, where it drives the 12mhz crystal filter.
Source resistance there is around 200 ohms, so you'd get a bigger signal than at the 50 ohms of T5 pin 5.
T5 presents a DC path to ground, so no need for the RF choke shown in the above link.
The 45mhz filter at Y1 limits the bandwidth to something reasonable for AM, as Farhan has previously noted.
Might work better if you remove the load presented by X2 and X8 somehow.

Output of the diode detector would drive the preamp at Q70.
I'd remove C50 and drive the base of Q70 from the diode detector through a series 1uF cap.

The germanium 1n34a is ideal because it has a very low forward voltage drop, to receive low level signals.
A Schottky diode like one side of the BAT54s diodes used in the uBitx will work, but is not so sensitive.
The cheap 1n34a's out on ebay are Schottky diodes at best.
A good source for a real 1n34a is:? ?

Problem is, not enough gain in the front end of the uBitx to drive the simple diode detector
for anything but the strongest incoming AM signals.??
You could add another RF amp specifically to drive the diode detector, tap the signal from Q32 to drive this new amp.
Maybe just duplicate the Q30,Q31,Q32 amplifier.
I'd be tempted to try a cheap MMIC such as this:???

Or you could move on to the next page of that tutorial link above and think about implementing a synchronous detector.
You can sort of receive an AM signal with an SSB receiver by carefully tuning it in, but tuning is very tricky.
The BFO must sit right on top of that AM carrier or you will get a beat note, and no matter how close you are the phasing won't be ideal.
A synchronous AM detector makes your SSB receiver's BFO synchronize with the incoming carrier, so tuning locks in when you get close.?

Disclaimer:? I haven't built an AM receiver since messing with a chunk of galena and a cat-whisker
some 55 years ago.

Jerry, KE7ER