My advice is to pare-down the receiver to the bare minimum for troubleshooting purposes. In this case, I'd pull capacitor C8 out of the circuit (lift one leg, etc.) and break the R8 connection at the mixer diode anodes. This leaves you with band-pass filter (BPF), a pair of mixer diodes, the 50 to 600 Ohm impedance step-up network (L3 & C12) and a pair of headphones. 
 
Now, I'd like you to temporarily attach a radio-frequency choke (RFC) of 1 to 4mH (value not critical) between both mixer diode (D4 & D5) anodes and ground. Attach a radio-frequency (RF) signal generator between this same node and ground. In other words, I'd like you to initially get the receiver working using an external RF signal generator without any added circuit complications. 
 
Of course, your RF signal generator should be set to the 80m CW band. The output level should be at least a couple, or three, volts peak-to-peak. The exact level isn't critical; you simply need enough signal-level to "decisively" switch the diode-pair on/off. As for the diodes, I used a pair of 1N4148 Silicon signal diodes taken from my junk box. 1N914's, etc., would work as well. It's not necessary to match these diodes.
 
Right, so tune-up the BPF, connect a full-size 80m antenna and you ought to be in business. A step-attenuator in-line with a second RF signal generator may be used to measure the minimum receive sensitivity. Otherwise, wait for the 80m band to open in the evening and have a listen. 
 
I ought to point out something that is critical; namely, there must be a DC return to ground at both the mixer beat-frequency-oscillator (BFO) port and at the audio-frequency (AF) output port. In my schematic, this condition is produced at the BFO port by the DC path through R8 into the secondary of T2, and then on to ground. If this DC circuit were broken - for example, by inserting a series capacitor in the path - the mixer would cease to function. Likewise, the headphones provide the necessary DC path to ground at the AF port. The mixer would not function properly if a capacitor were to be placed in series with the headphones. 
 
At the same time, there must be no DC path to ground at the RF signal input port. Please notice in my schematic that C8, C10 and C11 provide this required isolation. 
 
Once you have the receiver working to your satisfaction, then you can remove the temporary RFC and begin reconnecting the various components; C8, R8, T2/C6 and C7. 
 
I mention on my web page that T2 and C6 ought to be slightly "mistuned" in order to produce the RIT function. More importantly, this tuned circuit shapes the signal from the one-transistor BFO. The mixer needs to be supplied by a BFO signal having roughly a 50% duty-cycle. The output taken from T1 is too distorted to produce good mixer operation without the inclusion of this tuned circuit. That's also why you didn't need T2/C6 when you were using a (clean) BFO signal from your bench RF signal generator in my above recommended test setup .  
 
The operation of this mixer is relatively simple. When the BFO input signal goes negative, both diodes become reverse-biased and promptly turn-off (think of these diodes replaced by two opened SPST switches). In this case, the BFO “sees” an open circuit and the input RF signal energy is free to pass into the headphones. 
 
When the BFO input signal turns positive and climbs past the diode's internal barrier-voltage threshold (~0.6V for Silicon diodes), the diodes will turn-on together (think of both SPST switches as closed). Now, both the BFO and the input RF signal are simply shorted to ground. 
 
In either diode state (open or closed) the BFO energy is prevented from passing into the antenna. That's it! That's how a pair of unmatched diodes can be used to build a commutating, single-balanced mixer.
 
Please don't worry about trying to find the exact set of headphones that I use. If you have a reasonably sensitive pair of 600 Ohm magnetic headphones then you should be set. Different values of headphone impedance may be accommodated by tweaking the impedance matching network values at L3 and C12. Oh, and don't use piezoelectric headphones with this receiver without adding a parallel RFC to ground (in accord with the above-stated, DC path requirements).