Have an 85(stock), 4x4, extra cab, purchased truck new, with leaf springs which are sagging. Depending on what I have loaded in truck I have 1-2 inches of movement before bottoming out on the rubber bumpers.

Have four leafs in front, all same thickness, and four leafs in back, one thick leaf and three thinner ones.

Thinking of having springs re-arc'ed to oem specifications but don't know what oem spec is. My Toy maint manual is silent on spec and have yet to locate this type info. on this web-site.

Re-arc shop would likely re-arc to what-ever I asked, but I would like to have an end-picture with a little more clarity.

Any ideas on how to ID the oem specs?

Alot of posts in the past with this same situation.
Most who do pay to have re-arched are disappointed 6 months to a year later because the leaves go back to sagging.
Here's an alternative method, especially if you haul stuff alot. Fixed my rig just dandy.
http://www.gearinstalls.com/dc.htm

Clicking on the link provides photos that appear to be all on the rear of the truck. Was the front end handled the same? With possibly slightly lighter coils?

if you have solid axel in front Im sure you could use the same technique.This worked great on the rear of my 86,but I havent figured out how to apply it to the ifs.I used the helper spring kit from autozone,jc whitney etc... just pitch the hardware that comes with it and tack them in on top.Ive been thinking some kind of coil over shock would work on front but I havent wanted to pay for it yet.

The coil thing would be too tricky for the front IMO. Your best bet for the front would be to add some $45 add-a-leafs.

The only issue with AALs up front (assuming stock steering) is there is no room for more leaves without the draglink and steering j-arm hitting the springs/u-bolts. 4 was the most leaves I could stuff under mine. Might be able to swap a stock leaf for something stiffer. Front springs were pretty much flat in stock form, best option is to get something like a 2" lift spring from OME.

That's what I was going to suggest. The "shortest" springs you can get from Emu. The guys at Wimberley 4 wheel drive ( on 35 just south of San Marcos) are dealers for OME I think.

My '86 sags pretty bad in the back and I was thinking about getting them rearced and adding an extra leaf. This would bring it back to spec. and the extra leaf would keep it from sagging again. Any thoughts on this?

Sure, no need to re-arch is adding a leaf. The Rancho Soft-Ride AAL kit is pretty good:
- http://www.gorancho.com/

Comes with a long thin leaf and a shorter, thicker leaf you can mix and match with your existing leaves to make up a custom pack.