I've installed a FiTech in my in-law's Truck. It runs quite well but the interface is pretty clunky.

When it's time to put one in my Warlock, I'll give Holley a try. A huge amount of the installation troubles are user induced, primarily around RFI/noise and adjustments that need to be made by the user.

I'd recommend buying a factory refurbished Sniper for $800. Add the Hyperspark distributor so you can control timing and you'll be all set. You'll also need a high pressure pump. In tank is preferred but that might not be an option on a pickup truck.
https://www.holley.com/products/fue...refurbished_-_sniper_efi/parts/FR550-510

I sell and support Holley EFI. I DO answer the phone too!

how does the sniper system act with 260/270 duration @ 50 cams ?

do you still support FAST also, the biggest piece of crap ever produced, that I spend thousands ,because you also supported, all I ever heard from them was your out of warranty,as my quad driver failed twice,and flooded the motor .... met with u at Carlilse years ago and you had no answers,and I was not the the only one, every one was having problems, you just blew it off.....PATHETIC....

What about mounting the Sniper to a Performer. I also saw a vid where a duel plane screws with the MAP sensor. Have to add a spacer or cut down the intakes divider. Is this true?

Yes - sort of. Dual plane manifolds were made to generate a signal that a carb needs, but TBI EFI systems don't need that. And EFI needs a map signal that represents the entire map that the engine sees, which is more consistent when using an open plenum. An open spacer or a cut down divider is a way to do that when you start with a dual plane manifold.

FAST was one of the leaders 10-15 years ago and their higher end XFI products still work, and yes I am one of the ONLY people that still answer the phone and I will support a FAST user if they have one of the higher end products. FAST made a mistake with the lower end systems. There's nothing I can do for an EZ user where I cannot get into the software. 99.9% of my sales are other products, such as Holley, but I still want to help if I can. So I actually DO answer the phone and I'm proud to be known for that.

So, is there a standard rule for the amount of space the throttle body needs?

That's a tuffy. Any amount of opening helps, but there is no magic number because camshaft parameters affect it. There are thousands of Sniper users out there that never did anything about their dual plane manifold and they are running fine. Sorry to be vague but it's the truth. Use a single plane if possible is all I can suggest.

The question is sort of irrelevant to the EFI used. I am running a Microsquirt system with dual 1bbl TB's on a reproduction dual 1bbl intake for my flathead six. I had to make a 1" adapter to mount the throttle bodies to the intake and I tapped both adapters to feed a common source to the MAP sensor. With the 4bbl TBI setup you still need a common vacuum source but it doesn't have to be anything huge, just enough to tie both sides together. A thick gasket may do the trick. Pic shows my setup to feed the MAP, if you had stack EFI you'd still need to tie all eight setups together to provide a common source.

That's a tuffy. Any amount of opening helps, but there is no magic number because camshaft parameters affect it. There are thousands of Sniper users out there that never did anything about their dual plane manifold and they are running fine. Sorry to be vague but it's the truth. Use a single plane if possible is all I can suggest.

Yep. Many people do that and are okay. Too bad you don't have enough space for a 1" spacer.

When you run this air cleaner and plan on using the air box as well things are real tight AND the neck is already cut down on the base...

Holley also has a EFI forum that is broken down by specific model lines like Sniper, HP or Dominator. There are also numerous Holley EFI Facebook pages that get tons of traffic with technical advice and questions.

Most of the race tracks I go to I see the majority of the cars running EFI conversions are all Holley. So you are more likely to run into other people that are familiar with Holley than the others in my experience.

Do what was suggested above. Pop a small hole in each side of the manifold below the carb pad and link them together with tube. Tie that to the map sensor. This assumes you have a separate map instead of an integrated unit.

I believe the Map Sensor in internal to the throttle body