What is the clearance required for this to fit? Looks fairly large, but pictures can be deceiving.
Each DOA board is 1.28 inch x 1.05 inch (32.5 mm x 26.8 mm), so just a bit bigger than an APP992 for 2520 socket or a 2520 clone.
The bigger dimensions are for layout needs, since the APP992 v2.1 has a unity gain product of more than 40 Mhz the layout is important, and however, is better designing a good layout since the sound depends even by it.
I have not changed the same layout of the original APP992 but I have added only a few of tracks that has been needed.
Regarding clearance, is important to say that the two DOA boards can be kept over the near parts around avoiding shortcuts just by using the right lenght of the DIP socket pins.