Yes! You will have to pull the oil pan to get the timing cover off.
It is a pain to have to do this, but they are neat engines I think.
Here are some pics from my 1991 truck(s)....it is the same exact engine but your 1989 has a different style distributor......yours has a vacuum adv. to it whereas the 90-93 do not. Your computer is a one year only also, because of this, so if it is messed up, you'll need to get the one for that 1989 year, or have yours repaired by AvPro or another company like them.
The computers in these trucks (1989-1993 G6 computers) have 2 capacitors in them that will leak and cause corrosion on the ECU board......only the original capacitors leaked, if the computer is repaired, it will be fine from then on. You can remove the computer from the truck (under the pass. side kick panel) open it up and look at the board to see if it has any corrosion.
I have pics of mine I can post up if you need to see them.
Here are a few pics of the engine from my 1991 B2600i 2WD truck so you can see what your getting into. It will be a good father & son project for you two! And if ya need any help, just holler!
Get the FePro or Mazda head gasket when you put it back together.
The FelPro has an orange O-ring for the oil passage nipple that supplies oil to the head and rocker assembly....this O-ring is almost the same size as the fuel injector O-rings....but not quite! It's nice to have it a certain color to differentiate it from the inj. O-rings when you get a complete gasket kit!!
More of the oil pickup tube, and the main reason for you to have to remove the oil pan to get the front timing cover off!
I think it's easier to pull the engine rather than laying under the truck on my back so much, but I do have the tools to do this also.
And some other pics.
Keep us posted and if you need help, just ask! Oh, BTW, just click or right click the pictures and you can "open" the image so it is full size then......a little easier to see then! And welcome to the forum!!