Ive been running the FItech (power adder 600hp version) with timing control and a tanks inc tank/Walbro pump for two years or so now. I've learned a few things.
The throttle body EFI should work fine with a stock intake manifold. I can't imagine any interference issues there. But you should block the heat crossover.
I cant say if it would clear a stock dual snorkel air cleaner, I've never tried that.
Tanks Inc will also sell you a matching sending unit and in tank fuel sender/pump when you buy the tank. They offer three different Walbros for different power levels. Stock appearance isnt much of a concern here, the only visual difference from a stock tank can't be seen after installation.
You'd absolutely have to run an aftermarket distributor with a phasable rotor to run timing control. I use the MSD, there's also a knock off version that works fine if you want to save some money. Here's a very helpful thread from Johnny at Pace Performance discussing distributors.
https://www.forcbodiesonly.com/mopar-forum/threads/fitech-efi-question-and-answer.27076/If you decide to modify your stock tank, you MUST add baffles. If you try to run EFI on a non baffled tank, you'll suffer fuel starvation anytime you have less than a half tank of fuel. But the aftermarket tanks are (relatively) dirt cheap compared to the labor of modifying your old one, you may be well buy new.
And I strongly recommend going in tank versus external fuel pump.
The 3/8th fuel feed line is fine, but the 1/4 return line is a definite NO. The car would run with that, but you'll burn up fuel pumps very rapidly. A 5/16 return line is a bare minimum, but 3/8 return is ideal. There's minimal price difference between the two sizes, and you have to buy one anyways, so go for the 3/8 return.
And make absolutely sure your hard fuel lines are made of steel, not aluminum. I'm sure yours are likely steel, but it's one thing you must be 100% sure of for safety.
As for the sniper EFI, I worked on a friend's impala last month with the basic Sniper setup, and learned that it doesn't retain memory if the battery is run low. He had left his lights on by accident, and when he went to start the car afterwards, the computer had forgotten everything. Not just the tune, but basic setup. Engine size, cam size, cylinder count, etc. That was extremely annoying to reset everything the next day.
I don't know if that applies only to the entry level sniper, but that was very annoying. It turned me off of their product after that.
Make sure to use ethanol resistant braded hose (or EFI fuel line) at each end of the hard lines. Modern ethanol fuel can eat through the rubber lining of cheap braded hoses in no time.
I'm sure there's more I'm forgetting, but those are the highlights. If you're on the fence, I say go for it. After two years and 15000 miles, I've enjoyed quick starting regardless of outside temps, not returning the old carb for weather changes, consistent performance, silky smooth throttle response, and my favorite, no more raw gasoline exhaust smell. I can drive the car for hours now and get out not smelling like fuel.
Hope this helps.