The Y8 ECU is pretty similar to the GSR ECU, the big difference being the program in them. Really the hardware is almost indentical, except for the knock sensor board and the extra output for the secondary runner control. For example, OBD1 P28, P30, PR4, P72, P74, P75 area all almost indentical except for minor parts differences and the programs they use..
You won't hurt anything with the GSR ECU, and it will probably run rich, and it isn't tuned for your engine. Hopefully no lean spots showed up that could damage anything..
Stick with the stock ECU, just like everyone else says..