I've never used an EFI tech unit before but I have heard good things about them.  For me, the price tag is too high.  No disrespect, but you mentioned in your description that you don't know what your ignition timing is.  If it was me, I'd spend some time and dial in the 600 cfm Edelbrock carb you have and also your timing curve.  Is your vacuum advance can hooked up on the distributor and working?  There is no reason that a well tuned 350 with a carburetor shouldn't be getting 16 - 18 mpg.  If you are getting 7 to 9 mpg, then something is not tuned correctly.

The total timing for a SBC with the vacuum can unhooked should be 36 to 38 degrees advanced.  You will need to know how much mechanical advance your distributor has in order to set your idle timing.  Idle timing + mechanical advance should equal 36 to 38 degrees.  You can buy an advance timing light for about $100 bucks or even cheaper second hand on Kijiji.  After your timing is set and locked down, then hook your can up for the vacuum advance to the manifold port on your carb and it will pull extra timing at idle and when your car is not under a load.  This will help fuel economy and give you lots of power off a stoplight.

After the timing is set, borrow a hand-held wideband O2 sensor from somebody and weld an O2 bung on your exhaust just past the header or cast manifold, whichever you are running.  You will need to do this anyway if you plan on running EFI because the whole system relies on the wideband O2 sensor.  Drive your car and see where it is running rich.  From the factory, Edelbrock runs pretty big jets and rods because they don't want you running lean and wrecking your motor.  Too rich is a problem though and will give you poor mileage and potentially wash cylinder walls.  You will probably see once you install an O2 sensor that you are running rich at idle and part throttle and possibly even WOT.  This will mean a rod and jet change which is about 30 minutes of work and about $30.  Edelbrock will have a chart for your carb telling you what rod/jet combo to run if you want to lean it out a stage or 2.  

Just my 2 cents.  Rather than spend $ on an EFI, I'd spend some more time dialing in what you already have.  Even if you switch to EFI, it won't run well if you don't have your timing sorted out.

mate in new zealand put fitech on his bigblock. Bloody awesome. Self learning, fully programmable. Just do it. Get a control centre which has pump etc. i put EFI on mine. Really good. Installed an aeromotive stealth in tank fuel pump system. Adaptable. Only downside? I guess with carb and dissy spares can be carried in the boot In case of failure