You didn't specifically state what engine you are converting to GM TBI. You will have to get some signals such as distributor reference pulses to the ecm. If the engine has a hall effect type distributor, you may be able trigger a GM ICM with it.
This may help you on fueling. http://www.gearhead-efi.com/Fuel-Inj...BPC%29-on-7747
You will need to know the flow rate of the injectors in the throttle body you have. http://www.gearhead-efi.com/Fuel-Inj...d-part-numbers

The following text is from from the TunerPro XDF file from the $42 mask which is used on the 1227747:

If other than stock engine, injectors and fuel pressure use the Injector Sizing Spread Sheet to calculate BPW!
http://www.gearhead-efi.com/Fuel-Inj...ull=1#post2589


TBI:
Val = 1461.5 * (VOL/RATE)
VOL = Vol of 1 Cylinder in liters, (0.7125l)
RATE = Injector flow in gms/sec
5.7l = 7.71 gms/sec (61.2#/HR)
(VOL/RATE) = 0.0924 l/gm/sec

Cylinder volume and injector flow rate are combined in this calibration value. A typical value for a 5.7 liter V8 is 135.

Cylinder volume is 5.7/8 or 0.7125L

Injector flow rate is 7.48 grams/sec, (61.22#/hr/injector)

Using the formula BPW = 1461.5 x (cyl vol / inj flow rate )

= 1461.5 x (0.7125/ 7.71 )

= 135

Two more threads with relevant info:
http://www.gearhead-efi.com/Fuel-Inj...Engine!-HOW-TO!
http://www.gearhead-efi.com/Fuel-Inj...BI-Conversions!