I just put a Sniper EFI on my '90, and I used a surge tank from RobbMc. It has the high pressure pump in a ~2qt can, and is slosh-proof. I installed it under the hood where the charcoal canister used to live. No need to upgrade your tank, or build any type of high pressure pump rail underneath your rig. I can't recommend the surge tank method enough.
1990 Grand Wagoneer with HD towing package -- everything works! (for now...)