What year did the mono-leaf glass springs go away?

[Rod's Trucks]

Title (mostly) says it all.
I have a '98.
I know the mono-leaf diff housing is slightly different where the leaf springs bolt up. What should I look for, to see if it is ( or confirm it is not) the mono-leaf axle assembly? Is it just the width between the spring mounting holes, or is there something else I should be measuring to determine compatibility?
I cannot really get good measurements on my axle assembly, but probably could If I knew what specifically to look for.

I have a spare 3.73 axle assembly with a good ring and pinion , but cannot read the code on it to determine what year it came from. The code is there, but I cannot make it out well enough to make an educated guess.

I am thinking of installing an Eaten Tru-Trak in the spare housing and to do the install and setup the shims. I have installed different ratio R&P's many years ago in competition cars, but it is tedious and I do not need to rush it. I could take my time in the dry warm shop without disabling the van for days or weeks. I would be able to do the axle and pinion bearings, if needed, and change the seals at my convenience.
When ready, then I would swap the whole assembly in one operation.

[M_a_t_t]

I think 94 maybe early 95. The mounting perches are different widths. I think the fiber glass ones are wider than the steel ones.

[AstroWill]

https://sites.google.com/site/astrosafa ... enerations
95 was the last year, and they were optional. The difference is the spring perch.
You can replace or modify the perch to work with the narrower steel springs https://www.astrosafari.com/viewtopic.p ... 00#p723162

Whatever you do, if you modify the wider perch, don't take off any material from the vertical sections, that is what gives it strength.