Thanks for the encouragement. Your suggestion caused me to look a little harder. The Corvette sensor would have been difficult to fit, but I found another sensor with the same resonant frequency, plus it is the same pipe thread as the 250's block drain. It fits 1992-1992 G20 Chevy Van 5.0L and a few others. I like the fact that it will just screw in without bushings or machining. I pasted the product description below.
Amazon lists it as: Delphi AS10014 Ignition Knock Sensor. $34.79.
DELPHI KNOCK SENSOR -- 38.1 mm diameter, 21.84 mm hex size, 5500-6400 Hz frequency, 100 K Ohms resistance, 1/4-18 NPTF dry seal thread size; A high quality, direct fit OE replacement knock sensor.
