Been playing with my push in drive shafts (i've got three sets - one properly shortened with the diff ends missing, one normal and one from my diff that i've cut down to get an idea of length required).

Started to remove the diff side joint today off a the spare shaft so i could put it on the shortened shaft that was missing a joint. Found out tonight that my diff and therefore original joint (not touched yet) has a smaller spline than the one i removed.

So, if i remove the joint from my original (small end) drive shafts - will they fit onto a drive shaft that had originally a large end?

Are their limitations between the small and large drive shaft splines?
Are their rules how much engagement the spider joint must have?

There is a "How to" on the Sierra owners club or Crust world.
You need the thicker diesel push in shafts to put the Lobro on.
We have tried putting the lobro flange in a push in diff, the left hand flange touches the planet wheel shaft locking the diff, a couple of mm milled off may free it but the circlip groove is getting a bit close by then.
I don't see why you could not turn down the planet wheel shaft but it becomes a bit of a mission.

Ah, no, i'm not trying to convert from push in to bolt in shafts. My shafts are ALL push in. I want to know if i can interchange thick diff splined push in with thin diff splined push in shafts.

I had something similar as I want to put a 6.5inch Sierra diff into my car. This has smaller tripode joints than the 7inch tripodes. In my case the splines on the shaft are the same and the CV joints are interchangeable.

You may have sensed caution in my tone. The reason for my caution is that Lars (from here) tried to use one of my driveshafts (or bits from it) on his car that also has a push-in diff, and they didn't fit. I guess this means I know less about this than I thought I did.

I think the answer to your question is "yes they are interchangeable".

Matt