I have the Holley analog system on my Wag. It is open loop. The Wag had it installed when I bought it about 3 years ago. I have had no problems with it (even the TPS), but I do not like the lack of tuning capability.
I just ordered the parts to build a fully digital ECU for the system, which will use all of the existing Holley (GM) stuff, just replacing the analog control and wire it in, I will add an O2 sensor also. This will allow me to monitor and program the fuel delivery with a laptop computer while the engine is running. I'm really looking forward to this mod, and hope to get it done in a month or so. With this setup, I should be able to adjust the fuel deliver for max power or max efficiency (mpg) depending on what I want. You should be able to put a system together with parts from a junked GM product for much less than the Holley setup. Of course you may want to decide if it's something you would be able to do on your own.
For information on the controller and other EFI stuff:
P.S. I also have a new Mallory HyFire ignition control to install, as I'm now having occasional problems with the OE icm.
I'm hoping I can increase the mpg a bit when all is complete.
89 GW, 360, MegaSquirt Fuel Injection, Edelbrock manifold, TFI,Mallory HyFire VIA ignition module, Rusty\'s 4\" lift,Rancho RS9000\'s, RS9700 remote now installed (still leaks, but setting now lasts longer), 31 x 10.5 Hi-Tech Re-Treads, Bulldog remote start and keyless entry