put the knock filters together for a little comparison... i probably should have grabbed the 3.1 MEMCAL, but i can do that later if necessary....

http://i.imgur.com/AJKnl5J.jpg

the MEMCAL with the 27SF512 in it is the 91-93 version, the one with the factory PROM is the 94-95. note that the size of a few components changed, but otherwise they all seem to be in the same location. some portions of the traces stayed the same, but that changed quite a bit too.... notice that the blue layer can have both traces above and below it on both. i have to wonder what the little component is in the center.... seems like it would be an IC, definitely something custom made for Delco. lots of laser-cut resistors too.

have to wonder how difficult making a DIY knock filter would be..... doing the bandpass calculation(for a given bore size) isn't too bad, but then just have to figure out a way to ground the circuit that signals knock to the processor.... and then having a method to allow for sensitivity adjustment...