'87 mustang 4 cyl to 5.0 swap

This falls under 5.0 tech.
Thread moved.

cheap, fast, and reliable.
pick two and call it a day.
do a search there is tons of info out there that would take too long for me to post here. there is also a sticky in the useful technical thread index.

Sounds like you have the basic easy to find stuff. The harder to find stuff that you need are

Trans harness: Runs from left kick panel through trans tunnel to transmission. Simply unplugs

5.0L Fuel Lines: They run on the passenger side the 4cyl runs on the driver side.

5.0L Headlights harness: The alternator wiring is run with that. The 5.0L alternator plugs are on the passenger side and the 2.3L plugs are on the drivers side.

Fuel pumps: 5.0L and 2.3L are the same. Mine is running perfect with the 2.3L fuel pump....upgrade if you do heavy mods

Dash Harness: They are the same. Mine still has the 2.3L dash harness. All the plugs for the clutch pedal box are there. They simply have a removable jumper wire in the auto harness that you remove when swapping to a manual.

Driveshaft: The yokes are different.

What year is your 5.0L stuff from? Some have fuel pump relays in different locations that make it a little difficult to get running quickly.

the main 5.0 harness that goes through the firewall replaces the 2.3 harness. it should be plug and play. the easiest thing to do would be to remove every harness from the 89 and swap it over to the 87. the dash harness can stay, but all the underhood stuff should go. if you label everything it shouldnt be that hard, just tedious. it sounds like a lot, but it's a hell of a lot easier than splicing in old 2.3stuff. the car I own now has spliced 2.3 harnesses all over it and it's a bitcj. this winter I am ripping all of that out and replacing it with factory v8 wiring.

http://forums.stangnet.com/showthread.php?t=516785

This sticky covers the swap pretty well.