OK, I've asked and gotten no repsonses elsewhere locally, so it's time to ask my Yota family.
What backspace do I need/should I use? I have 3.75 and 4.75 available to me. What is stock? I know sooo little about back spacing.

 

Stock is 4.75":



All you wanted to know about backspacing, track width and more:

http://www.4crawler.com/Diesel/Tires.shtml#WHEELS

 

Thanks Roger, I believe you posted the same answer the last time I asked here. The link now explains it a little more for me. So, 3.75 will move the tire further in, correct?
Anyone here (there must be!) running 3.75 back spacing? Got pics? I'm soooo confused.

 

Now, I reread the link and am more confused. Someone simplify this for me, smaller number, tire sticks out further, larger number, tire tucked in further, correct? That being said, 33x12.50 TrXus on 8" wheels with 3.75, will that fit my '92? Currently has that TrXus' on the stock 7"ers but looks a little silly (narrow).

 

If you look at this exact section of the page:
http://www.4crawler.com/Diesel/Tires...ningTrackWidth

it should be pretty clear:

For each 1" less backspacing or 1" increase in offset, the outside of the wheel will be 1" farther out from the vehicle

And in yur exact case, 7" -> 8" wheel is 1" wider (per side) and 4.75" -> 3.75" is 1" wider (per side) so the outside edge of the tire will be 2" (i.e. 1" + 1") wider than it is now. To answer your own question (will it fit?) take a tape measure or 2" long scrap of wood and run it around the outside edge of the tires in various positions of turning and compression and see if 2" wider will affect anything, interference-wise. Worst case is usually front tire fully compressed and turned fully.

 

Thank you again Roger, I see clearly now. So my track would be 4" wider, wow, that sure would change things. 3.75 it is! Will have to check for clearance issues first though.