TBI for GMC 454

The item you're looking for is the Rochester TBI-220.  It appeared on everything from the 4.3L V6 up to the 454, with the difference between all, being the injector size.  Off the top of my head, I believe the injectors fitted were something like 28lbs/hr in the 4.3, the 305 were 32, the 350 was 40, and the 454 were 45lbs/hr.  fuel pressure was either 12 or 15psi on these units.

But wait, Dave... how could they use the same throttle body- that'd be way too big for the little six, or way too small for the big V8...

Yeah, but no.   It's possible for the throttle bore to be too small for the 454, but in a throttle body or injection system, there is no circumstance where having too LARGE a bore will cause the problems commonly associated with 'overcarbeuration', because the throttle body's function is simply to limit the amount of airflow INTO the manifold.  Fuel metering is not done by a venturi, it's simply a throttle plate... the fuel volume is managed by the ECM (in yours, it's referred to as '7747')  based on manifold absolute pressure (MAP), throttle position sensor position, crankshaft RPM, coolant temperature, and (when in closed-loop mode) the 02 sensor.

Now, there's a device on it called an IAC... an Idle Air Control valve.  It is a stepper motor with a leadscrew and a plunger on it.  The plunger moves in and out... opening or closing off a passage that bypasses the throttle plates.  When running at idle the throttle plates will be fully closed off (there's no 'idle stop'), the idle bypass circuit, the IAC plunger, and motor bypass whatever air is necessary to maintain proper idle.

 My Friend, Dave Kamp,,,,,,,,It good to hear from youse!!  Many THANKS for responding!!

  Altho,,,,Ahem,,,altho,,,,I say this with a generous amount of depredations at the apparent amount of possibilities of even one little thingie being the culprit amongst all the possibilities this system has that can be the bad boy ,,,,,? My memoriy has been joggled to bring back many tales of other TBI owners being exasperated with the system,,,,,

 My question is this,,,,With the correct distributor,,,UM,,,"pre-computor",,,an adapter plate for the manifold, that will accept a simple Holly of 750 CFM or even a (gasp) AFB,,I believe Edelbrock markets them old AFB's now a days,,,would this "modification" give a fellar a lot less headache with it's simplicity,,,???