Small Block Distributor Recommendation

You are kind of asking 2-3 questions in 1 in the original post.

Are you replacing you ignition because your current setup is giving you issues? or are we fixing something that isn't broke?
if your box is toast, or you're replacing a dead ignition? There are many distributors that will run just fine, in ready to run fashion for well under $100.

or is the question, "what distributor do you need to #1:run a sniper #2 control timing with said sniper???

my 2 cents, as we just started offering an ignition line...and i'm very familiar with the sniper, and pro-billet ignitions.

your best bet on controlling timing, with a sniper, is to keep the distributor you have. Not only is it endorsed by holley and MSD to work with a sniper, but not a single option you listed #1-4 is compatible with timing control on a sniper. (your #4 is not timing control compatible w/o taking it apart and swapping in a completely different ignition module)

so #5. Buy a sniper, and an msd#84211 rotor...read up on rotor phasing, and read the sniper 550-510 instructions online. Your msd you already have is easily your best option.
the sniper can be used to drive a coil, so your 6AL box can go if you want to use the sniper to control timing.

please call holleys tech line if you'd like to confirm the above. your # 1-3 are not sniper compatible on a consistent basis at all, and your #4 will only control timing with taking the distributor back apart and installing a 2 wire module.

i would observe from your question you were just ready to spend a few hundred bucks on a distributor that would actually place you further away from an EFI conversion than you are now....so take that few hundred, throw it down on a sniper, and you're in a better place.

hopefully that helps your decision!