I forgot to add that a few years ago I purchased a holley avenger throttelbody self tuning fuel injection unit.
I ran it in my 253 Hq ute . At the time it cost around the 2k mark including freight. I found it easy to setup and reliable. But as you can appreciate there was no real improvement in fuel economy over the 465 holley it replaced.
Where it did shine was in its drive ability cold start and other features like being able to set the electronic kickdown to what ever % of throttle desired.
aircon shut of at a given rpm or throttle position. Thermo fan's triggering and engine load compensation etc.
All these features accept the auto tuning can be altered on the delco pcm .It is a little more fiddly with the basic tuner pro software but if you go the tuner pro real time tuning with a modified pcm
and a wide band oxygen sensor you'll get all the benefits of a good factory system .
There are also a number of similar systems if the desire is for a factory carby look some of which are hard to tell that they are not carbys. Ie no fuel rails and very little wiring with the computer mounted on the throttle body its self.
Before you decide do a search for retro fit efi . There are a bunch of them (FAST EFI) (PROFECIONAL PRODUCTS) (HOLLEY)(EDELBROCK) to name a few.
There is also the option of a crate motor direct from GM complete with a pcm and cat converter package specifically designed and tuned to conform to epa standards for the retro fit scene