obviously you'll need a timing light
hook it up to the battery and put the inductive pickup (no idea if thats the right name im mad tired) on the #1 plug wire. start the truck and shoot the light at the harmonic balancer and the timing marks should line up. then you can unbolt the distro and turn it to advance or retard the timing.
and these are off the FSC forums,
"Some '87's had TBI, and maybe those had no vacuum advance, like my '88. These would also have the computer wire (at the passenger's side firewall, brown w/ black stripe, I think) that needs to be disconnected at the connector. It's a black connector about the size of a AA battery, that comes out of the wiring harness at the top of the firewall.
Is this a TBI?
The connector you speak of is on the driver's side, runs in conjunction with another harness just under the brake booster. it's a single wire plug. just unplug it to bypass computer's adjustments, set timing to 0 degrees, plug it back in, and you're good to go."
i personally didnt have to anything like that with my TBI 262 when i replaced my distro.
hope this helps man