Speaking of competence... I just noticed that I have a bug in the block diagram. The output stage is actually a composite amp with a high-speed, high-current output. I'll fix it and update it in the post above (and on my website).
And me thinking that there are paralleled OPA1656 under the heatsink.
Given that you already designed and implemented probably the best measuring "gainclone" from Earth, I would say that there might be a couple of LM3886TF under the heatsink. A similar approach was done by Lake People inside G-103 where they used LM1876TF, so at least my guessing seems plausible.