I'm a bit late to the party on this, but I did actually try a Holley Sniper EFI on my Pantera at one point when I still had the old engine in it and it was problematic due to a number of reasons. Holley, and probably all of the other vendors selling similar systems, loves to bill them as a simple drop-in conversion that you can install on any car by basically throwing the box at the car right off the UPS truck. There is a lot more to the installation, however, and a lot more you have to take into consideration.
First, you must be absolutely sure of the state of your engine before you put the EFI system on the car. Any issues you may have with your car now are not going to magically go away with the Sniper system. In fact, it will likely make them worse. Part of my problem with the old engine in my Pantera was a bad build from the early 2000's done by a prior owner. Undersized pistons for the engine resulted in slap-happy movement within the cylinders and ultimately led to bad compression on cylinders 5, 6, and 8 with the other cylinders being perilously close to bad compression. Not knowing what camshaft was in the car was another issue, as the build invoice from 2001 showed some generic cam being used, so we had no idea what lift and duration was. Long story short, you will want to do all you can to ensure your engine is in good working order with the setup you have now.
I actually went with the full Holley Sniper EFI system at the time, including their HyperSpark distributor, control box, and coil so that their EFI computer controlled the engine timing as well as setting redline. If you go for the whole system like this, you'll need an MSD tach adapter to convert the signal from the Holley system to something your tach will understand, and you'll also want to make sure you use the same type of distributor gear on the Hyperspark distributor as is on your current distributor. Irrespective of what you plan on doing regarding ignition timing, you will absolutely need to ensure that your coil is located as far away as possible from the actual Sniper unit. The Sniper ECM is located on the throttle body and is subject to RF interference generated by your coil and you can expect some problematic behavior when the two are in close proximity to each other. If I were to do another EFI system on my car, I'd actually go with something where the ECM was a separate unit that could be located somewhere more sane. Also, a slightly irrelevant sidenote is that the Sniper has a noticeable intake hiss during more "spirited" driving.
Apologies for the wall of text, but that's effectively my experience with the Sniper EFI system on a Pantera. My case was a series of bad circumstances that ultimately led me to a year long overhaul of the whole car and a brand new engine. I'm sure the Sniper EFI system works great when all of the other variables you have to consider are good and I can't really say it's an overly bad system.