I used the factory style hard line, Hemi sized 3/8 supply and bought a regular BB/SB 5/16 line for the return and ran them side by side. I flared the factory line with the GM push-on style o-ring fittings and bought the appropriate adapters. For example Russell Performance 644133.
AG.

General rule of thumb is that the return line should be no less than the diameter of the feed line.

I agree100% !!!!! but others will say you can use 1/4 in return

Rich recommended a 3/8 return line but now I’m trying to figure out if I can use my Rev N Nator or not. Rich says he’s never even heard of one lol. I bought the hyperspark distributor. He said I should be good using my firecore wires and coil.

On EFI applications the return fuel is under little to no pressure compared to the supply so it can tolerate a smaller line. I wouldn't push my luck though on a 1/4" line though.

EDIT - Also, with some EFI setups you can PWM control the pump so you may have very little return flow so that makes running a smaller line way more feasible.
AG.

Does it have a points in connection? When the Sniper controls the timing the control works thru the white wire which connects to the points in connection on the ignition box. MSD and Holley ignition boxes have spot to connect the points output. If you have that on your box then you are good to go. Either look at the box or look at the instructions.

The Rev N Nator is a replacement MP style ECU that requires the magnetic pickup distributor to work, the Holley won't be able to control it unfortunately if you're looking to control timing from the Holley.

I'm researching this stuff myself, I already have a 6AL and Blaster II coil, was going to use the points output from the Holley to drive the MSD box. If I were you since you need to replace everything and already bought the Hyperspark distributor, I'd buy the matching Hyperspark CDI box and coil. You won't have a ballast resistor in line with the 12v feed to the coil anymore.

https://www.holley.com/products/fue...er_efi/hyperspark_ignition/parts/556-151
https://www.holley.com/products/fue...er_efi/hyperspark_ignition/parts/556-152

The Rev N Nator is a replacement MP style ECU that requires the magnetic pickup distributor to work, the Holley won't be able to control it unfortunately if you're looking to control timing from the Holley.

I'm researching this stuff myself, I already have a 6AL and Blaster II coil, was going to use the points output from the Holley to drive the MSD box. If I were you since you need to replace everything and already bought the Hyperspark distributor, I'd buy the matching Hyperspark CDI box and coil. You won't have a ballast resistor in line with the 12v feed to the coil anymore.

https://www.holley.com/products/fue...er_efi/hyperspark_ignition/parts/556-151
https://www.holley.com/products/fue...er_efi/hyperspark_ignition/parts/556-152

Correct. If the EFI pump is sized correctly then the return line should not have much pressure in it so it can be smaller. All the EFI cars that I've plumbed lately have used a regulator in the trunk (race cars) or the regulator is in the tank (street cars) so I don't use a return line anymore. The OEM guys don't use return lines.

I agree with that. If you already have MSD stuff then keep it but if you're buying new then I'd go with the Holley Hyperspark ignition box. The MSD boxes cost more because they have extra features such as rev limiter chips but you don't need any of that stuff when you are using the Sniper since it is all built in.

Plugs depend on which head you have and what the compression ratio is. I use NGK 6987 on all my street builds but I also always use a Trick Flow head. I haven't used a cast iron head for more than 30 years so no idea what plug would work with them.

Then the 6987 should work for you. Those are a wide gap, extra projected nose plug. They are OEM fitment on several newer cars and are usually around $3 each from Summit or NGK direct.