sent the vendor for megasquirt some questions about a week ago, haven't heard back. doesn't inspire a lot of confidence...
be that as it may, i managed to get an ecu #89661-2440 for $100. plugged it in and it seems to work, but at first the engine wanted to idle very low to the point of stalling and being hard to start cold with no throttle. seems to run fine at running temp, test drove through all gears. there is something that looks like a vacuum switch on the top side of the engine that is buzzing, which i don't recall buzzing with the old ecu.
from what little i can find, the main difference between this unit and the 89661-2430(1) is that it is wired a bit different some slight sender/engine improvements and preparing for obdii. it will run a 1994 engine ok, but the cel will not go out. but i still don't get a cel signal from this other ecu (plug A, pin 6, blue with yellow stripe wire).
if it will run ok on this ecu, ill send the one it came with to jet performance for a refurbish. now that i can get a closer look at this unit, it's looking like it is, in fact, a #89661-24230(1). it looks like they changed the colour of the print on the label, and had a second label with a large "30" on it.