When I was first looking at an engine for my SLC I gave an EFI some thought and made a few calls to Holley among some of the other EFI manufacturers. In general, the sales staff are really not versed well enough to help to any real extent with high compression and big cam engines. So after a lot of phone calls, I finally got an engineer on the phone at Holley by telling them I needed some support on a "NASCAR type race car engine" They had me call back to another number and I talked to someone that knew enough to convince me that he was the best I was going to get on the phone.
The first thing he wanted to know was how much intake manifold vacuum I had at idle. When I told him it was around 8-12 inches of vac that jumped around with the big cam. He said right away that any of the self-learning throttle body type systems like the Sniper or the Atomic will not work and that I need at least the Terminator type but he wasn't sure that would be the best choice, I really should use an individual port injector type system (LIke NASCAR) or either the HP multiport kit or the EFI-R system. He also was very clear that tuning these systems wasn't intended to be done by a first-timer and that I should seek a profession shop with a lot of experience.
The big takeaway is the EFI-R system allows for the very precise mapping needed to replace the wide range of vac signal missing in a radical cam engine, The wide vac range is required to allow the self-learning systems enough variation to derive a fuel map from. That would be something on the order of at least 16-18 inches of vac. 10 just gets you an on-off fuel map that just can't regulate fuel requirements at part throttle or low load power requirements and doesn't work.
Here is what is needed to complete the individual throttle body type system.
That IS a LOT of money. I did a Proform 750. Works well.