round up a friend to help....

remove distributor from engine....

remove spark plug from #1 cylinder. hold your thumb over the spark
plug hole while your friend bumps the starter a little bit at a time.
(like you just turn the key to engage the starter and as soon as it
turns the engine over you turn the key off) you do this until you feel
pressure in the #1 cylinder which tells you the piston is coming up
towards TDC on compression stroke. (you are turning the engine over a
little bit at the time, so you can stop when the timing mark gets
close to zero at the harmonic balancer)

A good tip is to take some white out or other white marker and mark
the timing line on the harmonic balancer where you can see it better.

So once you feel pressure you then can take your thumb off the head
and slowly bump the starter over until you can get the timing mark
close to zero (at the harmonic balancer). If you mess this up...start
the whole process over again.

Place distributor with the rotor pointed toward #1 cylinder which also
has to correspond to the number one plug wire on your cap. This does
not have to be exact but it does have to be fairly close.  ON the
firewall near the accumulator you need to disconnect the ECM timing
wire which allows you to set base timing. Start truck with wire
disconnected and adjust base timing to 0 degrees. (timing light
needed).  Shut engine off and tighten distributor hold down clamp and
re-connect ECM timing wire.  The allows the ECM to control the timing,
like its supposed to, you cannot adjust the timing on these truck with
that wire connected, because the timing you want to set is the "base"
timing. You cannot modify the advance (that's what the ECM controls)

You'll need to clear the ECM codes by disconnecting the battery for
about 5 min and you should be good to go.

IF the truck backfires you are doing something wrong, or if it pops
through the throttle body you have done something wrong.  

You have to set timing when #1 piston is at TDC, therefore the
distributor has to be in the correct "phase".... if you get this off
the engine will backfire and generally run like crap, it will be
pretty obvious. Also you need to set the base timing like it says on
the sticker under the hood which on my 92 says 0 degrees (350 engine)
I you don't get this right the engine will run like crap too, because
the ECM assumes the base timing is set at 0 degrees and therefore it
advances the timing based on that....so plus or minus here can make
the ECM advance the tinning either too much or too little.

If you removed the plug wires from the distributor you need to make
sure your firing order is correct on the distributor and starting from
plug wire number one make sure the plug wires are in the correct
order.

The distributor will "sit down" flush ....so if there is a gap at the
base of the distributor and the engine you are wrong.  You can't
shortcut the business about TDC on compression stroke and setting at
the proper base timing (with wire unplugged).

I'm no expert but I've been a few rounds with my 92 K1500 350 when
I've changed the intake gasket and also one time when I replaced the
distributor. Get the timing mark as close to zero at TDC on the
harmonic balancer...install distributor with rotor pointing to number
one piston and number one spark plug wire on the cap and you should be
ready to start and set base timing.

I'm played this game a number of times and you'll hear different
stories on the same theme but this is what works.  The only really
good shop manuals are the GM ones...the others tend to leave important
details out or just skip over various things.

Popping through the throttle body or backfires are a good clue that
the timing is off.....start from zero and do it again...unless you are
experienced at this the assumption is that you've screwed up something
so its best to start the process from zero and try again.

Hope this gives you some help....I know this can get really
aggravating...I've been there a number of times myself.

Of course you'll need to replace the spark plug you removed and
reconnect the spark plug wire before you start the engine. Its also
good to leave the wiring disconnected from the distributor so the
engine does not start before you are ready to do so, since on these
trucks you generally have to climb in under the hood and so it becomes
a  safety issue.

-----------
Elbert
ask@me.com