Scrape all the gasket surfaces extra clean. Use a vacuum cleaner to suck up the gasket material as you go. Any gasket residue left on mating surfaces can cause leaks that are hard to find. Don't use a wire wheel on aluminum parts, it will remove metal quickly. Plan on changing the oil within 4 hours of operation once it is back together & running. This will give the engine oil time to wash all the gasket particles down into the sump or oil filter.
Plan on removing the distributor. Mark the distributor and engine block at the base with a screwdriver & light tap of a hammer. Line up the timing marks on the crank and then mark the place on the distributor housing where the rotor points.
Here's the alternate method for distributor removal:
Take the coil wire out of the distributor. Pull #1 plug, put your finger in the spark plug hole. Have someone crank the engine until it starts to blow air past your finger. Stop cranking, turn the engine by hand (breaker bar on the harmonic balancer bolt, or put the car in gear and push) until the TDC mark on the harmonic balancer lines up with the pointer on the passenger side of the engine. Loose the distributor hold down bolt, remove the clamp, cap and wires, disconnect the wiring harness. Pull the distributor straight up.
The following re-install depends on the engine being lined up as in the previous instructions.
To re-install, turn the distributor rotor to point to #1 cylinder position on the cap. The#1 position is about 11 o'clock if 6 o' clock is the front of the engine. Line the rotor up with it pointing at the #1 spark plug position on the cap and drop it in: you may have to twist the shaft some to get it to engage the oil pump shaft. Then remove the SPOUT connector plug, and use a timing light to set the timing. The SPOUT is the dangling connector on the distributor harness on stangs made prior to 94 and with a computer controlled engine. 10* is stock for most 5.0s' 12*-14* is good for more pep if you are not into NO2 or power adders.
My favorite trick that saves time and effort is the stay in place gasket. Be sure that you scrape (don't use a wire brush) all the old gasket material off, then clean all the surfaces with acetone or MEK.
When the surfaces are clean, use weather strip adhesive on the head to manifold surface, and on the side of the gasket that mates to the head. Follow the instructions on the tube or can and when it gets tacky, press the gasket down on the head.
Clean the area where the rubber rails mount to the block in front and in the rear with more acetone or MEK and do the same trick with the weather strip adhesive that you did to the heads.
Coat the rubber seals and the gasket area around the water passages with lots of Blue Silicone gasket sealer and put it together. Wala! no leaks, and no gaskets that shifted out of place.
If you reuse the injectors from your old setup, a repair kit is available from most auto parts stores if needed. Coat the injector body "O" rings with oil before you use them and everything will slide back together. Take the other advice you got here and run with it.
Fuel injector seal kits with 2 O rings and a pintle cap (Borg-Warner P/N 274081) are available at Pep Boys auto parts. Cost is about $2.74 per kit. The pintle caps fit either injectors with a pin sticking out the injector end or 4 with more tiny holes in the injector end. The following are listed at the Borg-Warner site (
http://www.borg-warner.com ) as being resellers of Borg-Warner parts:
http://www.partsplus.com/ or
http://www.autovalue.com/ or
http://www.pepboys.com/ or
http://www.federatedautoparts.com/
Most of the links above have store locators for find a store in your area.