I got my harness from a 93 GT for 100$, 200$ I've seen go for really good stuff, so if any of it looks rather worn try to talk him down.
Ford Fuel Injection is great... I got through most of the re-wiring of my harness in about 3 weeks with going to school and working. Shipping from them wasn't slow, at least for me.
Take your time with the harness and read up on everything on fordfuelinjection.com's site.
Fuel wise is a big debatable topic. Most people I've seen run a new line for the feed and the old line for the return. You can do this, or you can run whole new line (like what I'm doing, 3/8" alluminum tubing from summit), or just run lots of soft line, but that gets expensive.
You also have to choose what fuel pump style you will use. A lot of folks choose a frame rail mounted one out of a 80s model ford truck. This is easy and only requires the soldering of a return line to the pickup. The problem with this set up though is that is sometimes will uncover the pick up during cornering at low gas levels leaving your pump sucking air. Not good.
Another way is the constuction of a 'header tank' whereas a small sheetmetal or alluminum enclosure is built to house a standard 5.0 pump. This uses a second, low pressure pump, to feed gas into the housing so that the high pressure pump is always kept fed. Any sloshing will be so minimal in the header tank as to not uncover the strainer on the end of the 5.0 pump. The enclosure uses a feed line from the low pressure pump, then a feed line out to the engine. The return line also goes into the header tank to continue to replace fuel that is pumped out, lastly a return line to the fuel tank is used to alleviate any excess fuel that the header tank cannot hold. Problems with this set up are that the tank can be difficult to come buy for a novice, let alone construct, and it is complicated. (On this note, for followers of this method, how are the electrical connections passed through the wall of the tank? I mean, what do you use to keep pressure and gas from escaping and not grounding on the body of the tank?)
Third method can be considered the most drastic. This involves the placing of a fuel pump (5.0 type) into the stock gas tank. This requires a fair amount of modifying of the tank for how you do this. One member on here elected to build a baffled enclosure to drop into his tank. I personally am going to attempt to braze baffles into the tank in an attempt to utilize a modern drop in style arrangment.
Yes, unfortunately as tt670 said you will need a new distributer. Sell that one to someone locally and either get a new MSD or for more of a daily driver a junkyard or auto parts house one will work fine. Just be wary of the gear material selection, iron or steel. It has to mate right with your cam gear or you'll be doing alot more work than planned.
That's all I can think of for now.
The Swede