amc 20 twingrip tore down

 i tore down my amc 20 twin grip dif and found some surprising results checking it while i was dismantling.

No that shim itself won't come in a kit and you must match that shim thickness exactly - using multiple shims. (if that many come in a kit, I can't recall - can't remember what brand kit I last used.)
Pinion depth is important - so much so that AMC had a Kent Moore tool for measuring that, and spells out in the TSM how to arrive at the proper shim needs based on the pinion marks if you have to replace a gear set.

Imagine - how do people know those will break and how do they know how they get broken.... LOL

Anyway, on the play - I'll call it "rotational play" since end play is shoving an axle in and pulling it out and seeing what distance you get between the push and pull.

A prior answer was correct, but maybe not complete - there's play in the spines, but that should really be precious little - hardly noticable..... ah, but add to that the play in the gears inside the carrier - some call them spider gears, often books call them differential gears because they are what give you the "differential action" allowing the wheels to spin at different speeds - there is play between them, the tooth of this gear to the tooth of the next gear and then yet another gear. Add all that together, and don't forget the play of the spiders on the shaft that goes through the carrier and holds those gears - all normal. I'd say most likely - don't worry about it.
Add it all up - spines (shouldn't really be much but there is some) the differential gears as they interact, and the gears on the shaft through the carrier - it's called "stack-up of tolerances" if all each by itself it ok, maybe at the larger end of tolerance, but added together it's more than you may think.
There are cars out there, not AMCs, but any brand, operating on a lot of that sort of play - no problems.

Unless you've done a lot of 'em, you may wonder....... 

Think if this, too - what you are doing, spinning one wheel back and forth and feeling that play -it's not happening that way on the highway.
Normal operations will never "see" or feel that, only you, at one wheel, rear off the ground.

Not sure the style, year, etc you are working on, but the twin grip in my 73 has quite a lot of give between the axles when it's in the air, the one in my 70 Javelin you can't possibly move on wheel without moving the other - it's not possible unless you reach break-away torque.

I ask but i think that any amc 20 are all the same masterkits  even twingrips correct me if i'm wrong.

I would be glad if somebody could get me a fast answer on that so as i could order thanks